TECHNICAL REPORT on the REVIEW OF THE VIOLENT VIDEO GAME LITERATURE

TECHNICAL REPORTon the REVIEW OF THE VIOLENT VIDEO GAME LITERATURE

APA TASK FORCE ON VIOLENT MEDIA

TECHNICAL REPORTon the REVIEW OF THEVIOLENT VIDEOGAME LITERATURE

Task Force Members

Mark Appelbaum, PhD (Chair)

Emeritus Professor
University of California, San Diego

Sandra Calvert, PhD

Professor, Department of Psychology Director, Children’s Digital Media Center Georgetown University

Kenneth Dodge, PhD

Director, Center for Child and Family Policy William McDougall Professor of Public Policy Professor of Psychology and Neuroscience Duke University

Sandra Graham, PhD

Professor and Presidential Chair in Education and Diversity
University of California, Los Angeles

Gordon Nagayama Hall, PhD

Professor and Director of Clinical Training, Department of Psychology
University of Oregon

Sherry Hamby, PhD

Research Professor of Psychology Director, Life Paths Research Program Sewanee, The University of the South

Lawrence Hedges, PhD

Board of Trustees Professor of Statistics and Department Chair, Department of Statistics Northwestern University

APA Children, Youth, and Families Office

Lauren Caldwell, JD, PhD

Director

Amani Chatman

Program Coordinator

Dan Galloway

Intern

Effect Size Analyses

What Does the Research Say?

Summary

APA Task Force on Violent Media
TECHNICAL REPORT on the REVIEW OF THE VIOLENT VIDEO GAME LITERATURE

Available online athttp://www.apa.org/pi/families/violent-media.aspx

Suggested bibliographic reference:
APA Task Force on Violent Media. (2015). Technical report on the review of the violent video game literature. Retrieved from http://www.apa.org/pi/families/violent-media.aspx

Copyright © 2015 by the American Psychological Association. This material may be reproduced in whole or in part withoutfees or permission provided acknowledgment is given to the American Psychological Association. This material may not be reprinted, translated, or distributed electronically without prior

permission in writing from the publisher. For permission, con- tact APA, Rights and Permissions, 750 First Street, Washington, DC 20002-4242.

APA reports synthesize current psychological knowledge in a given area and may offer recommendations for future action. They do not constitute APA policy or commit APA to the activi-ties described therein. This particular report originated with the Task Force on Violent Media.

CONTENTS

Introduction
Literature ReviewProcess 02

Questions Emerging From the Meta-Analysis Review 02

New Literature 05

Systematic Evidence Review of the Literature Since 2009 05

Synthesis of the Evidence by Outcome 06

Synthesis of the Evidence for Other Research Questions 07

Preface

01 Appendix A:
Publications for Systematic

Evidence Review 19

Appendix B:
Characteristics Codedinthe
Systematic Evidence Review 27

In keeping with the American Psychological Association’s (APA) mission toadvance the development, communication, and application of psychological knowledge to benefit society, the Task Force on Violent Media was formed toreview the 2005 APA Resolution on Violence in Video Games and Interactive Media and the related literature. The goal of the task force was to ensure thatAPA’s resolution on the topic continues to be informed by the best science currently available and that it accurately represents the research findings directly related to the topic.

After consulting with the most frequently published researchers in the field, as well as prominent methodologists, theoreticians, and practitionersin behavioral science, pediatrics, communications, and public health, APA created a task force of seven senior scientists with exemplary methodolog-ical and scientific expertise to undertake a rigorous review of the literature. The task force members bring expertise in meta-analyses, child development, learning,digitalmedia,multicultural psychology,violence,andaggressiontothis effort. Task force members were Mark Appelbaum, PhD; Sandra Calvert, PhD; Kenneth Dodge, PhD; Sandra Graham, PhD; Gordon Nagayama Hall, PhD; Sherry Hamby, PhD; and Lawewnce Hedges, PhD.

APA adopted a multifaceted approach to the review of the science. Prominent scientists with broad expertise in related fields oversaw an inde-pendent evidentiary review and meta-analysis and review of the 2005resolution, augmented by input as needed from topical specialists repre-senting the range of viewpoints on the topic. The intent of this approach was to provide the most comprehensive, rigorous, and balanced review ofthe evidence base possible.

At the first meeting of the task force, the members spent significant time disclosing and discussing potential conflicts of interest. This process was modeled after the procedure used by the National Academies of Sciences

to eliminate potential bias in the group’s work. Specifically, task force mem-bers were asked to disclose and discuss any financial, scientific, or other interest that might conflict with their service on the task force if the inter-est could either significantly impair the individual’s objectivity or create an unfair advantage for any person or organization. Task force members were also asked to disclose any research or publication activity or commitment to a fixed position through public statement or publication or through other personal or professional activity related to the current task.

PREFACE

Video game use has become pervasive in the American child’s life: More than 90% of U.S. children play some kind of video game; that figure rises to 97% when focusing on adolescents ages 12–17 (Lenhart et al., 2008; NPD Group,2011). Although high levels of video game use are often popularly associ-ated with adolescence, children younger than age 8 who play video games spend a daily average of 69 minutes on hand-held console games, 57 min-utes on computer games, and 45 minutes on mobile games, including tablets (Rideout, 2013). Considering the vast number of children and youth who use video games and that more than 85% of video games on the market contain some form of violence, the public has understand-

knowledge to benefit society, the Task Force on Violent Media was formed toreview the APA Resolution on Violence in Video Games and Interactive Media, adopted in 2005, and the related literature to ensure that APA’s resolution on the topic continues to be informed by the best science currently available and accurately represents the research findings directly related to the topic. The task force was asked to consider whether a new meta-analysis was needed or whether an alternate approach to reviewing the relevant research might be better suited to achieving this goal. The review of the scientificliterature related to violent video game use is particularly important given

INTRODUCTION

ably been concerned about the effects of violent The public has understandably been concerned aboutvideogameuseonindividuals, especiallychildren
and adolescents. the effects of violent video game use on individuals,

News commentators often turn to violent video game use as a potential causal contributor to acts of mass homicide. The media point to perpetrators’ gaming habits as either a reason they have chosen to commit their crimes or as a method of training.

The media point to perpetrators’ gaming habits as either a reason they have chosen to commit their crimes or as a method of training. This practice extends at least as
far back as the Columbine massacre (1999) and has more recently figured
prominently in the investigation into and reporting on the Aurora, CO, theater
shootings (2012), Sandy Hook massacre (2012), and Washington Navy Yard
massacre (2013). This coverage has contributed to significant public dis-
cussion of the impacts of violent video game use. As a consequence of this
popular perception, several efforts have been made to limit children’s con-
sumption of violent video games, to better educate parents about the effects
of the content to which their children are being exposed, or both. Several
jurisdictions have attempted to enact laws limiting the sale of violent video
gamestominors,andin2011,theU.S.Supreme Courtconsideredtheissuein
Brown v. Entertainment Merchants Association, concluding that the First
Amendment fully protects violent speech, even for minors.

In keeping with the American Psychological Association’s (APA) mission to advance the development, communication, and application of psychological knowledge to benefit society, the Task Force on Violent Media was formed to review the APA Resolution on Violence in Video Games and Interactive Media, adopted in 2005, and the related literature to ensure that APA’s resolution on the topic continues to be informed by the best science currently available and accurately represents the research findings directly related to the topic.

1

The task force engaged in a three-step process for its work: (a) Identify the relevant literature, (b) review the literature’s findings systematically, and(c) synthesize the findings into coherent conclusions and recommendations.

LITERATURE REVIEW PROCESS

To undertake the literature review, we adopted a two-pronged approach toidentifying the literature to be included. First, we conducted a comprehensive search of PsycINFO, Medline, ScienceDirect, Social Science Research Network, ERIC, Google Scholar, ProQuest, Wilson Social Science Index, and miscel-laneous journals and references discovered through the search process. We used the following keywords: violent video games, violence, violen*, aggressive behav-ior, aggression, aggress*, prosocial*, prosocial behavior, computer games, video*, game*, and video games and media. We restricted the liter-ature to be considered to research focused on violent video game use separate from other forms of violent media to facilitate the review of the res-olution, which focuses on violent video games.

Although the four meta-analyses included some different articles and were conducted by investigators who held different perspectives on the impact of violent video game use, our review of the meta-analyses revealed similar significant effect sizes. All four meta-analyses reported an adverse effect of violent video game use on aggressive outcomes, with an effect size greater than zero and a narrow range of unadjusted effect sizes (.14–.29). However, the authors’ interpretations of these results varied considerably.

games, violence, violen*, aggressive behav-ior, aggression, aggress*, prosocial*, prosocial behavior, computer games, video*, game*, and video games and media. We restricted the liter-ature to be considered to research focused on violent video game use separate from other forms of violent media to facilitate the review of the res-olution, which focuses on violent video games.

All four meta-analyses reported an adverse effect of violent video game use on aggressive outcomes, with an effect size greater than zero and a narrowrange of unadjusted effect sizes.

Second, on the basis of an initial PsycINFO search, we contacted approx-imately 130 of the most frequently published researchers in the topic area torequest nominations of the 10 strongest empirically based articles addressing violent video game use published between 2000 and 2013. This process yielded four1 meta-analyses conducted since the 2005 resolution and directly rele-vant to the task force’s charge to evaluate the literature related to violence invideo games and interactive media (Anderson et al., 2010; Ferguson 2007a, 2007b; Ferguson & Kilburn, 2009). Given the number of meta-analyses already completed, we decided to carefully review these existing meta-anal-yses to determine what they addressed and how they converged or differed.

The four meta-analytic reviews that we identified examined the impactof violent video game use on a variety of negative outcomes (Anderson et al., 2010; Ferguson 2007a, 2007b; Ferguson & Kilburn, 2009). The meta-analyses reviewed more than 150 research reports, including more than 400 effect sizes. Although the outcomes considered differed somewhat across meta-analyses, aggressive behavior, aggressive cognition, aggressive affect, physiological arousal, prosocial behavior, reduced empathy and desensitization, and criminal violence were included in at least one

The search process yielded a fifth meta-analysis conducted since the 2005 policy statement (Savage & Yancey, 2008). However, we did not consider this meta-analysis to be directly relevant to our charge because it did not examine effects of violent video games separately from other forms of violent media.

QUESTIONS EMERGING FROM THE META-ANALYSES REVIEW

During the review of the meta-analyses, we identified six important issues that were not adequately addressed.

Is this research applicable to children?

The earliest research in this area focused primarily on young adults 18 years ofage and older and, more specifically, on college students. Young adults are a group of considerable interest because they have a high exposure both to vio-lent video games and to other risk factors for violence. Similar concerns have been voiced about the impact of violent video games on children and adoles-cents. Implications of this research are often applied to children, yet relatively few of the studies used in the meta-analyses reviewed included children or adolescents younger than age 16 as participants in the research.

2

Does this research address the developmental trajectory of potential effects or the possible course of vulnerability to potential negative effects?

Questions have been raised about whether children and adolescents are particularly vulnerable to effects of violent video game use. Prospective lon-gitudinal studies can provide information about the effect of violent video game use on children over time, as they age into adulthood. The value ofthese studies would be to elucidate how violent video game use affects the lives of participants in ecologically important ways. These studies would also provide estimates of the time period of effects and the trajectory of impact as the effects grow or decline across long periods. Finally, these studies can inform theory because they can be used to test hypotheses about mediators of impact (i.e., the processes through which effects occur) and moderators (i.e., individual or setting characteristics that alter the impact). However, the meta-analyses we reviewed included very few longitudinal studies, and noneof those that were included considered enough time points to examine the developmental trajectory of violent video game use and associated outcomes.

Do outcomes for males and females differ?

Video game use is often stereotypically associated with males; however, nearly all teenagers—99% of boys and 94% of girls ages 12–17—are exposedto video games (Lenhart et al., 2008). Although it is true that boys have historically spent more time playing video games throughout childhood than have girls, it appears that this gap may be narrowing (Lenhart et al., 2008;Rideout, 2013; Rideout, Foehr, & Roberts, 2010). However, a considerable difference still remains with regard to daily game users; this group is 65% male. Further, males are at higher risk of perpetrating physical violence (Federal Bureau of Investigation [FBI], 2013; Hamby, Finkelhor, & Turner, 2013). Including females in participant samples without analyzing potential gender effects may distort group findings. The meta-analyses reviewed did not consider gender differences in outcomes or collapsed across gender after an initial analysis of baseline differences.

Does the degree of exposure matter?

Some questions of policy importance focus on the issue of dose. The first is the basic question of whether individuals with greater exposure to violent video game use are more likely to show increased aggressive outcomes. A second is whether there is some level or threshold of exposure that marks a point of potential concern. In many of the experimental studies, a single dose of exposure is administered to every participant. In studies of violent video game habits, by contrast, it is more likely that exposure is indexed as a continuous measure on the basis of the reported frequency of exposure toviolence and magnitude of violence in video games. The meta-analyses did not address questions related to degree of exposure.

What is the role of other known risk factors for aggression in moderating or mediating the effects of violent video game use?

Research has identified a number of risk factors for the development of aggression, including factors at the level of the individual (e.g., aggressive traits, neurobiological factors, academic achievement), family (e.g., low socioeconomic status [SES], harsh discipline practices), peers (e.g., bullying, peer rejection), school (e.g., exclusionary disciplinary practices), and neighborhood or community (e.g., poor urban settings) (e.g., see Bushman, 2013). Children who experience multiple risk factors are more likely to engage in aggression (Dodge, Coie, & Lynam, 2006; Herrenkohl et al., 2000). Most of these factors were not tested in the meta-analyses we reviewed because an insufficient number of studies had included these other aggression riskfactors. Other moderation factors were included in at least one meta-analysis, such as duration of game use, and Eastern versus Western cultures (Anderson et al., 2010).

What is the role of other game characteristics?

In addition to the violent content in video games that may be related toaggressive behavior by game users, questions have arisen about other qualities of the experience that may influence aggressive outcomes. Someof these factors involve the properties of the video game, how the game is played, and the user needs that game use fulfills.

Properties of the game include factors such as the presence or absence of a plot and the production features used to present aggressive con-tent. Television programs and movies are often based on stories with plots that have moral themes in which the hero acts aggressively to save others and overcomes a desire for revenge and retribution (Calvert, 2015; Calvert, Murray,& Conger, 2004). The moral decisions of heroes in response to the aggres-sion of others, particularly in regard to their own feelings of revenge, provide a potentially redeeming quality to these experiences, as all humans grapple with the impulse to “get even” with those who have “wronged them” at vari-ous points in their lives (Kotler & Calvert, 2003). Comprehension of complex archetypal plots has implications for how youths perceive heroic characters.

Although early violent video games typically reduced the plot to a min-imum (Calvert, 1999), changes over time have led to an increased use ofcomplex plots, which require players to grapple more with their feelings and decisions about vengeance. For example, player actions in Assassin’s Creed II can lead players to feel guilty, and they are able to decide how much revenge they will pursue as well as how they assassinate other players (S. P. Calvert, personal communication, October 2014). Other violent video games explicitly involve taking on antisocial roles (e.g., Grand Theft Auto).

How the game is played involves the user interface (e.g., joystick, Wii remote, or player movements per se), the player’s perspective, and the use of competition and cooperation as ways to engage players in the game. Game interfaces have changed considerably over time; user activity was much more cumbersome in the past than at present (Przybylski, Rigby, & Ryan, 2010). Players also have a symbolic perspective during game play through their char-acters. First-person perspectives have been thought to impact players the most, as their perspective is that of the avatar, which may increase players’ identification with their character; by contrast, third-person perspectives treatplayers as more distal agents with control over their avatar (O’Keefe & Zehnder, 2004). Additionally, some researchers have suggested that competitive fea-tures of games produce the aggressive effects (Adachi & Willoughby, 2011).

User needs, or motivations for using violent video games, can include the satisfaction of three basic human needs: competence, autonomy, and relatedness (Przybylski et al., 2010). Based on the identity of the users, specific games may have differential effects on users. Additionally, perceptually salient production features and engaging plots can also influence how the game is played, leading to immersion in a video game program, which may enhance player enjoyment. To the extent that enjoyment increases, players may experience what is described as “flow,” which can facilitate sustained exposure to the violent video game over time. As exposure increases, deleterious effects of exposure, such as desensitization, may increase (Calvert, 1999). The role of these characteristics in the relationship between violent video game use and aggressive outcomes was mostly unexplored in the early literature.

To the extent that enjoyment increases, players mayexperience what is described as “flow,” which can facilitate sustained exposure to the violent video game over time. As exposure increases, deleterious effects of exposure, such as desensitization, may increase.

NEW LITERATURE

After fully reviewing the existing meta-analyses and identifying the issues detailed previously, we turned to the more recently published literature. Our review of this literature was designed to address two questions. First, does the more recent literature provide further evidence of the effects of violent video game use? Second, does the more recent research address the questions enumerated previously? To answer these questions, we used two techniques: asystematicevidencereviewandaneffectsizereview(meta-analysis) ofthe studies identified through the systematic evidence review as having suffi-cient utility to address our objectives.

SYSTEMATIC EVIDENCE REVIEW OF THE LITERATURE
SINCE  2009

We conducted a systematic evidence review of the literature published since the most recent meta-analysis to determine whether this more recent research sufficiently addressed the questions raised earlier in this report to supportconclusions about the effects of violence in video games. A systematic evi-dence review synthesizes all empirical evidence that meets prespecified criteria to answer specific research questions. This approach uses system-atic methods selected to minimize bias in order to produce more reliable findings (Oxman, 1993).

The Institute of Medicine and others have adopted systematic evidence reviews as a standard approach to summarizing bodies of literature to draw conclusions from a field of research (e.g., McGinnis, Gootman, & Kraak, 2006). A systematic evidence review includes the following: a clear set ofobjectives with predefined eligibility criteria used to include studies in the review; explicit methodology; a systematic search that attempts to identify all studies that meet the criteria; an assessment of the findings in the studies identified; a systematic presentation of the characteristics and findings inthe included studies; and conclusions based on the evidence review (Zief &Agodini, 2012).

To conduct the systematic evidence review, we repeated the literature search process described earlier to capture all relevant articles publicly available between January 1, 2009, and August 12, 2013. We identified 170 research reports, including gray literature (see Appendix A). Those reports were screened according to the following inclusion criteria we developed:

– Does the report include at least one empirical analysis addressing video game violence separately from other media violence?

– Does the analysis include complete statistics?

– Does the report include at least one of the outcome variables considered in the earlier meta-analyses: aggressive behavior, aggressive cognitions, aggressive affect, physiological measures, prosocial behavior, reduced empathy or desensitization, delinquency, or violence?

– Does the report include some measurement of violent video game exposure?

– Does the report include some description or assessment to determine thatthe violent video game is, in fact, violent?

– Was the study published in a peer-reviewed academic journal?

In establishing these criteria, we sought to create a body of evidence thatwould be extensive and directly relevant to our goal of identifying relation-ships between violent video game use and aggressive behaviors and asso-ciated outcomes and that would address whether those relationships are causal. Although we initially included gray literature in our screening, in partto answer concerns about the potential for publication bias in evidence, we ultimately decided that peer review would be an inclusion criterion. The ratio-nale was as follows. First, peer review provides a basic, independent indicationof quality. Second, by selecting peer-reviewed journal articles as our sourceof information, we also tried to standardize our unit of inquiry. Whereas the same information may be found in multiple conference proceedings, for exam-ple, it is less likely that the same study would be published in multiple locations. We examined these articles for all possible effects of violent video game use related to the outcome variables identified through the earlier meta-analytic review, including long-term, short-term, negative, positive, and null effects.

Of the 170 articles examined, 68 met all six screening criteria. These articles reported the results of 78 studies that were then each coded for study characteristics. Coded characteristics included research design and methodology, sample characteristics, violent video game exposure characteristics,

To assess the utility of the evidence provided by the studies, we rated each study on five dimensions for fulfilling the task force’s charge: possibility for causal inference, ecological validity, sampling validity, and measurement of independent and dependent variables. Each of the studies was randomly assigned to two members of the task force for rating, except those studies with neurological outcomes, which were all assigned to two members withtopic-matter expertise. Task force members rated each study’s contributionto the evidence base pertaining to the research questions identified in the earlier review of meta-analyses.

The studies were then divided into two groups: studies perceived as having sufficient utility and those perceived as having insufficient utility for informing the decisions and recommendations the task force was charged with making. Studies were assigned to the sufficient utility group if they were rated by at least one rater as having sufficient ecological validity, sampling validity, or possibility for causal inference to address the task force’s charge and no more than one of these variables was rated as having insufficient utility by the second rater. In addition, to be included in the sufficient utility group, the study had to have at least one dependent and one independent variable rated as having sufficient measurement validity.

SYNTHESIS OF THE EVIDENCE BY OUTCOME

Aggressive behavior

The link between violent video game exposure and aggressive behavior is one of the most studied and well established. Of the 31 studies reviewed,14 investigated the relation between violent video game use and aggres-sive behaviors. Aggressive behavior measures included experimental proxy paradigms, such as the administration of hot sauce or a noise blast to a con-federate, self-report questionnaires, peer nomination, and teacher rating ofaggressiveness. A positive association between violent video game use and increased aggressive behavior was found in most (12 of 14 studies) but not were assigned to the sufficient utility group if they were rated by at least one rater as having sufficient ecological validity, sampling validity, or possibility for causal inference to address the task force’s charge and no more than one of these variables was rated as having insufficient utility by the second rater. In addition, to be included in the sufficient utility group, the study had to have at least one dependent and one independent variable rated as having sufficient measurement validity.

We used three primary criteria for evaluating the measures in a study: validity, reliability, and precision. Studies that ranked high on at least one ofthese factors and low on none of the factors were rated as having sufficient utility. Studies that did not meet these criteria were assigned to the insuffi-cient utility group. Interrater reliability was high, and any initial differences of more than one unit were resolved by having both raters rescore the article. Study inclusion in the sufficient or insufficient utility group reflected the task force’s determination of the potential relevance of the study for answer-ing the specific research questions considered in this review. This ratingprocess yielded 31 studies published since 2009 with sufficient utility to be included in the synthesis of findings.

Next, we considered the evidence available for each research question, using the following four inquiries:

• –  Was there enough research to draw conclusions?
• –  What does the evidence suggest about a relationship between violent video game use and measured outcomes for children and adolescents?

The results of this synthesis are summarized below, organized by outcome variable.all studies published after the earlier meta-analyses.

This continues to be a reliable finding and shows good multimethod consistency across various representations of both violent video game exposure and aggressive behavior. The findings were also seen in a range of samples, including those with par-ticipants who were older children, adolescents, and young adults. They also showed consistency over time, in that the new findings were similar in effect size to those of past meta-analyses.

Since the earlier meta-analyses, the literature has broadened in some directions. For example, there are more longitudinal and multiexposure studies. The literature has also broadened in terms of populations studied, including a limited number of studies of children, high-risk populations, and non-U.S. samples, although more similar research is needed. Several longi-tudinal studies, using both experimental and naturalistic approaches, have helped establish that the effects of violent video game exposure last beyond immediate effects in the laboratory.

The results of this synthesis are summarized below, organized by outcome variable.

Several longitudinal studies, using both experimental and naturalistic approaches, have helped establish that the effects of violent video game exposure last beyond immediate effects in the laboratory.

Aggressive cognitions

Numerous laboratory and longitudinal studies have assessed the impactof violent video game use on aggressive cognitions, which includes both self-reports and direct measures of cognitive processes. Aggressive cognition measures included hostile attributions and expectations, word completion, Implicit Association Test responses, aggressive intentions, aggressive cogni-tions about the world being a hostile place, dehumanization, and pro-violence attitudes. These measures are important because they inform an understand-ing of the psychological processes through which violent video game use might have an impact on behavior.

Of the 31studies reviewed, 13included aggressive cognitions as an out-come. All of these studies showed an effect of violent video game use on increased aggressive cognitions, replicating the finding in the pre-2009 research. In general, this research utilized improved designs (e.g., exposure via timed computer presentation and better measurement of dependent vari-ables such as computer-recorded response times and implicit associations) and longer term follow-up with participants.

Aggressive affect

Thirteen of the 31 studies included aggressive affect as an outcome;all were experimental studies with adults. Aggressive affect measures included self-report questionnaires, picture-rating tasks, and experimen-tal proxy. Twelve of the 13 experimental studies that examined the effectsof violent video games on affect indicated negative outcomes for adults. The most common negative outcome was increased hostility or aggres-sive affect. There is also evidence of less emotional reactivity (increased emotional desensitization) as a negative outcome, which is often seen as a result of previous experience with violent video games. There were no nonexperimental, naturalistic studies of the affective outcomes of violent video use on adults. Also, there were no studies of the effects of violent video games on children’s affect.

Prosocial behavior, empathy, and desensitization

In addition to increases in aggressive outcomes, nine studies examined decreases in socially desirable behaviors following exposure to violent video games. In particular, prosocial behavior, empathy for the distress of others, and sensitivity to aggression were diminished after exposure to violent video game play (seven of the nine studies). Eight of these studies were experi-mental, and all but two of the studies included adult participants only.

Physiological and neurological outcomes

None of the 31 studies we reviewed used physiological measures as their pri-mary outcomes; however, eight did include physiological measures, and two reported neurological outcomes. Of the eight studies that did include physi-ological measures such as heart rate changes, skin conductance, and blood pressure changes along with other measures, five found an effect of violent video game exposure, and three showed no effect.

Two studies we reviewed examined neurological outcomes as a function of violent video game exposure. Although both found effects, there were too few studies to derive a finding related to neurological outcomes.

Taken together, the evidence in the recent literature for a relationship between violent video game use and physiological or neurological outcomes is insufficient to support a conclusion.

Delinquency and violence

Although the media and the public often ask about the association between violent video game use and delinquency or violence, only one of the 31 stud-ies we reviewed included delinquency or violence as an outcome. Thus, too little research has addressed these outcomes to reach a conclusion.

SYNTHESIS OF EVIDENCE FOR OTHER RESEARCH QUESTIONS

Age and developmental trajectory

The new literature added 10 studies with children and adolescents 17 years old and younger. There also continued to be substantial data on young adults18 years old and older (21 studies). As mentioned previously, there were two key questions regarding age. First, is there any evidence that violent video game use is associated with aggressive outcomes for children and adoles-cents? The studies including children between the ages of 11 and 17 varied inoutcome but supported overall the premise that the findings are similar foradolescents and young adults. There remains a dearth of studies on children younger than age 10.

Second, are effects of violent video game use stronger at particular ages or developmental stages? This question cannot be answered from studies included in our review, which rarely examined the variation in patterns across age groups. When studies did examine multiple age groups, they did not offerenough variance in participant age to paint a meaningful picture of differen-tial developmental impacts of violent video game use.

Gender

Of the 31 studies included in the evidentiary review results, seven included male participants only; nine did not analyze gender, though they had male and female participants; two analyzed gender and found no effects, leading the researchers to collapse gender in subsequent analyses; six used gender as a covariate; and only seven analyzed gender fully as a variable of interest. In short, more than half of the studies did not examine potential gender differences for outcomes related to violent video game use.

This approach is somewhat surprising. In particular, although many researchers either assumed no difference between genders or assumed thatmen will experience greater effects than women, few actually analyzed gen-der as a variable, or they used gender as a covariate in the analyses. When analyzed, the negative effects of violent video game use did appear for both genders. Nevertheless, another limitation of the current literature is thatpotentially different outcomes of violent video game use for male and female participants were typically not considered. Thus,

The effects of violent video game use were fairly robust even with the inclusion of third variables known to be risk factors for aggression. Four ofthe five studies supported this finding. Only one study reported that violent video game play was not associated with aggression once other risk factors were accounted for. Of three studies that tested for an interaction between a risk factor and violent video game use, only one documented a marginal effect of education level. Therefore, the research we reviewed offered littleevidence that risk factors moderated the effect of violent video game use on aggressive outcomes. As in previous meta-analyses, researchers who con-ducted the studies in our review have been concerned with risk factors that no conclusions are possible regarding gender effects in this domain because a proper examination of this variable was lacking.

Degree of exposure

Another limitation of the current literature is that potentially different outcomes of violent video game use for male and female participants were typically not considered.

The largest body of evidence on the question of whether the degree of exposure has an impact on the effects of violent video game use comes from the non-experimental studies that assessed violent video game habits among participants (seven studies). Many naturalistic studies used a continuous measure of violent video game use (frequency of violent video game use, degree of violence in frequently played games, or both) and tested the linear association with violence. Five of the seven studies supported the model thatmore violent video game use is associated with higher levels of aggressive outcomes. Only a few studies examined a dose–response relation or height-ened effects among heavy users of violent video games. Therefore, the cur-rent evidence base cannot yet specify a particular amount of exposure thatclearly marks a problematic level of exposure.

Other game characteristics

As in the earlier meta-analyses, other violent video game characteristics thatmight influence aggressive outcomes such as plot, action, pacing, user inter-faces, perspective, and motivations for use remain understudied. Our review included insufficient studies to derive findings about these or any other game features. Given the literature documenting the effects of such features with other media, research examining the role of these characteristics in vio-lent video game use effects might increase our understanding of the criticalaspects of the games that contribute to negative effects.

EFFECT SIZE ANALYSES

In addition to the syntheses discussed previously, we also conducted effectsize analyses of the 31 studies identified in our review as being of sufficient utility to compare the earlier meta-analytic reviews with the review of the more recent literature.

Although we attempted to extract effect sizes from all of the studies in the sufficient utility group, we were only able to compute effect size estimates from 18 of them. The major reason that effect sizes could not be computed forsome studies was that they did not report the relevant results in sufficient detail. This is not necessarily a deficiency of the study—some studies were primarily focused on questions other than the impact of violent video games (e.g., they might have focused on the mechanism by which game use affects outcomes rather than the simple magnitude of the effect).

Other known risk factors

Five of the 31 studies we reviewed included consideration of other known risk factors for aggression. These analyses examined a variety of risk factors, including antisocial personality traits, delinquency, academic achievement level, parental conflict, child and parent depression, and exposure to deviant peers. The predominant strategy in these studies was to use risk factors as covariates in analyses of the effect of violent video game exposure on aggres-sive outcomes. The overarching question was, once all of these known riskfactors for aggression are accounted for, does violent video game use inde-pendently predict aggression? Three of the five studies tested for moderation whereby the interaction between violent video game use and one or more riskfactors was examined.

We computed the effect sizes as the difference between the mean out-come among the treated group (e.g., exposed to violent video games) versus the control group (e.g., exposed to nonviolent video games), expressed in(within-treatment group) standard deviation units, sometimes called Cohen’s d. Note that different studies used somewhat different outcome measures, and the effect size measure is designed to put all of the mean differences (treatment effects) on the same scale. We chose to use the metric of Cohen’s d because many of the studies were experimental, and it is the most common metric for use with experimental studies.

In addition to coding effect size estimates, we also coded the variances of the effect size estimates that were used for meta-analysis. There are two statistical models for meta-analysis, known as the fixed-effects and ran-dom-effects models. They differ in whether they treat the variation between studies as random error and may lead to slightly different combined results.The results we obtained from fixed- and random-effects methods were not substantially different, so we report here the results of the random-effects analyses because they tend to be more conservative.

We conducted meta-analyses using both fixed- and random-effects meth-ods for all of the studies and separately for studies with each of four outcomes(aggressive behavior, aggressive cognitions, aggressive affect, and physiolog-ical arousal). These outcomes were the only ones that were measured in atleast three studies for which we could code effect sizes.

Some of the earlier authors of the meta-analyses expressed concern about the potential for publication bias and used methods to adjust for its potential effects. Consequently, we computed several adjustments for publication bias, including trim and fill (Duval & Tweedie, 2000) and nonparametric weight functions (Hedges, 1992). Because results were similar, we report here only theresultsforthetrim-and-fill methodbecausethiswasthemethodusedinprevious meta-analyses.

Note that the earlier meta-analyses used the r (correlation coefficient) metric, while the current meta-analysis used the d metric. Consequently, we converted the results of the previous meta-analyses into the d metric (and con-verted our results into the r metric for reference using a standard method; see Hedges & Olkin, 1984). In all of the tables that follow, we present the standard error of the combined effect size in the current meta-analysis as a measure ofthe statistical uncertainty of the combined effect size. In comparing the results of the several previous meta-analyses with these new analyses, we did not use a strict statistical significance test but rather looked at general qualitative

agreement. However, we note that if significance tests were carried out and Bonferroni methods were used to adjust for multiple testing, none of the differ-ences would be statistically significant at the .05 level.

Table 1 reports the results of our meta-analysis of all studies examin-ing the effects of violent video games, combining across outcomes. In thisanalysis, we used a single effect size estimate per publication. If a study had more than one outcome, we took the average and used this as the (synthetic)effect size for that study. Table 1 also reports the average effect size esti-mate from one of the previous meta-analyses that corrected for publication bias. Note that a 95% confidence interval would range from approximately 2 standard errors below the average effect size estimate to 2 standard errors above it, or from about 0.21 to about 0.42. Because the results of each of the previous meta-analyses also have statistical uncertainty, we regard the aver-age effect size of 0.31 and its confidence interval of 0.21–0.42 as consistent with previous estimates.

Table 2 reports the results of our meta-analysis of all studies examining the effects of violent video games on aggressive behavior. Table 2 also reports the average effect size estimate from three previous meta-analyses, with cor-rections for publication bias if they were available. Note that a 95% confidence interval would range from approximately 2 standard errors below the average effect size estimate to 2 standard errors above it, or from about 0.19 to about 0.56. Because the results of each of the previous meta-analyses also have statistical uncertainty, we regard the average effect size of 0.37 and its confidence interval of 0.19–0.56 as consistent with previous estimates.

Table 3 reports the results of our meta-analysis of all studies examin-ing the effects of violent video games on aggressive cognitions. Table 3 also reports the average effect size estimate from three previous meta-analyses, with corrections for publication bias if they were available. Note that a 95% confidence interval would range from approximately 2 standard errors below the average effect size estimate to 2 standard errors above it, or from about0.11 to about 0.46. Because the results of each of the previous meta-analyses also have statistical uncertainty, we regard the average effect size of 0.34and its confidence interval of 0.11–0.46 as qualitatively consistent with the previous estimate of Anderson et al. (2010), but perhaps not with Ferguson’s (2007a, 2007b) two estimates, which were somewhat larger.

Table 3. Results of Meta-Analyses for Aggressive Cognitions

Table 5 reports the results of our meta-analysis of all studies examin-ing the effects of violent video games on physiological arousal. Table 5 also reports the average effect size estimate from three previous meta-analyses, with corrections for publication bias if they were available. Note that a 95% confidence interval would range from approximately 2 standard errors below the average effect size estimate to 2 standard errors above it, or from about 0.15 to about 0.91. Because the results of each of the previous meta-analyses also have statistical uncertainty, we regard the average effect size of 0.38 and its confidence interval of 0.15–0.91 as consistent with previous estimates.

Table 5. Results of Meta-Analyses for Physiological Arousal

Meta-analysis

Anderson et al. (2010)aFerguson (2007b)aFerguson (2007a)New studiesa

k rdSE

95 .170 0.345
7 .360 0.772
12 .250 0.516
8 .166 0.336 0.064

Meta-analysis

Anderson et al. (2010) aFerguson (2007a)aNew studies

k r

29 .135 4 .270 3 .189

d SE

0.272
0.561
0.384 0.265

aDenotes meta-analyses with corrections for publication bias.

aDenotes meta-analyses with corrections for publication bias.

Table 4 reports the results of our meta-analysis of studies examining the effects of violent video games on aggressive affect and empathy or desensi-tization. Table 4 also reports the average effect size estimate from a previous meta-analysis that looked at these two outcomes separately. All analyses cor-rected for publication bias. Note that a 95% confidence interval would range from approximately 2 standard errors below the average effect size estimate to 2 standard errors above it, or from about 0.04 to about 0.34. Because the results of each of the previous meta-analyses also have statistical uncer-tainty, we regard the average effect size of 0.19 and its confidence interval of0.04–0.33 as consistent with previous estimates.

WHAT DOES THE RESEARCH SAY?

Taken as a whole, the research included from the systematic evidence review
of the newer literature and the previously conducted meta-analyses was of
sufficient utility, variety, and scope to support certain findings about vio-
lent video game use. Notably, the findings are comparable across all of these
meta-analyses, including the one conducted by this task force. To draw con-
clusions, we had to consider plausible alternative explanations for effects
found and plausible explanations when no effects were found. This was
simpler when multiple research designs—experimental, observational, or
longitudinal—were used to study the same relationship between variables – The research demonstrates a consistent relation between violent video game within one age group. Research that included methodological and statistical controls for alternative explanations was also useful. However, for outcome variables for which the research did not include multiple well-controlled experimental studies as well as correlational methods, it was difficult to reach conclusions about the relation between violent video game use and those outcomes.

To develop our conclusions, we considered the review of earlier meta- analyses and the results of our systematic evidence review and effect size analyses of the more recent literature. All pointed to the same conclusions, providing confidence in the findings. As with most areas of science, the pic-ture presented by this research is more complex than is usually depicted innews coverage and other information prepared for the general public.

CONCLUSIONS

methods, it was difficult to reach conclusions about the relation between violent video game use and those outcomes.

-The research demonstrates a consistent relation between violent video game use and increases in aggressive behavior, aggressive cognitions, and aggressive affect and decreases in prosocial behavior, empathy, and sensitivity to aggression.

In interpreting the results, we kept in mind that aggression is a complex behavior with multiple risk and contributing factors. There was no expectation that violent video game use might be the only influence on aggressive outcomes or that it would necessarily be a stronger or larger influence than other known risk factors. We examined the research to determine whether violent video game use is a possible unique contributing – The research converges across multiple methods and multiple samples, with factor among other known influences on aggression.

multiple types of measurements demonstrating these relations.

We considered many factors in developing our conclusions, including the –

The recent research demonstrated that these effects hold over at least quantity, variety, and utility of the research from which they came. Several different studies from different researchers using different research populations, designs, and measures needed to be available for a conclusion to be developed. Also, any consistent differences in research outcomes support-ing and not supporting the finding had to be considered. The research we reviewed ranged widely in methods, samples, country of inquiry, discipline of author, and number of unique authors.

some time spans. This body of research includes laboratory experiments examining effects over short time spans immediately following experimental manipulations and observational longitudinal studies.

– Laboratory experiments have generally found a significant impact of exposure to violent video game use on aggressive outcomes. The experimental method increases confidence in the causal impact of violent video game use, but the controlled environment of most experiments reduces their ecological validity.

– The relation between violent video game use and heightened aggressive out-comes remains when other known risk factors for aggression are included
as covariates in analyses. However, this body of research is small, with a limited number of studies addressing a limited number of risk factors.

– Although the number of studies directly examining the relation between the amount of violent video game use and the degree of change in adverse outcomes is still limited, existing research suggests that higher amounts of exposure are associated with higher levels of aggression and other adverse outcomes.

UNDERSTANDING THE LITERATURE

What do effect sizes mean?

A substantial component of the recent debate on the existence and impor-tance of the effects of violent video game use has rested on an argument over effect sizes and their meaning. The two major viewpoints in the field (simply put, that effects are well established and substantial vs. that such effects have not been demonstrated to be large enough to take seriously) seem torest substantially on the interpretation of the effect sizes established in two different but overlapping meta-analyses (Anderson et al., 2010; Ferguson, 2007a). Although these two previous meta-analyses have produced effectsize estimates that are remarkably similar (rs = .19 and .15, respectively)— and were replicated in the meta-analysis on the newer literature conducted for this review—the interpretations of the importance of effect sizes of thisorder of magnitude vary enormously.

The estimation of effect sizes has become increasingly common in reporting the outcome of behavioral studies (usually reported in combination with some confidence interval) and for special and important purposes in applications such as meta-analysis. Despite the growing use of effect size estimates, the interpretation of effect sizes in absolute terms is not well established for two reasons. First, most effect size metrics are standardized indices, which permits them to be comparable even though they might be computed from vastly differ-ent outcome variables—which is the case in the meta-analysis of the effects ofviolent video games. However, the standardization makes their interpretation difficult because the effect sizes are not expressed in natural units.

Second, effect sizes express the magnitude of the relationship between variables. However, the effect size itself tells nothing about the value ofchange in the dependent variable to be achieved by manipulating the inde-pendent variable. Whether an association, and therefore the effect size, is judged to be meaningful depends on how easy it is to vary the independent variable and how important the dependent variable might be. A small effect of an independent variable that is easy to change (e.g., taking a baby aspi-rin every day) on an important outcome (e.g., death) might be judged quite important, but a large effect on a less important dependent variable might be judged less important.

The interpretation of effect sizes depends on the cost associated with pro-ducing the magnitude of change to the independent variable represented by the effect size weighed against the benefit received from the corresponding change in the dependent variable. At a minimum, then, the relevant question is, does the benefit from the amount of change represented by effect size x out-weigh the cost for a change of that magnitude? Applied to violent video game use, the interpretation of the effect size might be determined, for example, by asking whether the (effect size x) reduction in the likelihood of increased aggression outweighs the cost in lost access to violent video games necessary to bring about the reduction. Because this analysis requires a subjective judg-ment, the interpretation of effect sizes will remain subjective, dependent on the value placed on these considerations and the context in which the change tothe independent variable would occur. Debate about their meaning will always be possible.

The guidelines offered by Cohen (1988, 1992) as values for small, medium, and large are sometimes cited as standards for interpreting effect sizes. These guidelines, however, were developed for a totally different purpose—for attempting to power a study (i.e., to determine the number of participants thatmight be needed to detect effects of certain sizes) when no other pertinent information was available. The guidelines should not be applied to determine value of an effect size; it is not their purpose.

One also needs to remember that the effect size estimates computed formeta-analysis are exactly that—estimates. They are statistics with sampling distributions and standard errors. Because they are not population values, the estimates should always be interpreted in light of their statistical uncertainty (e.g., by confidence intervals) and not discussed as though they are known values.

Definitions of aggression and violence as outcomes

The violent video game literature uses a variety of concepts, terms, and defi-nitions in considering aggression and aggressive outcomes, sometimes using violence and aggression interchangeably or using aggression to represent the full range of aggressive outcomes studied. This lack of precision has con-tributed to some debate about the effects of violent video game use. In part, the numerous ways to consider violence and aggression stem from the multi-disciplinary nature of the field. Epidemiologists, criminologists, physicians, and others approach the phenomena of aggression and violence differently than psychologists and emphasize different definitions of the phenomena accordingly. Some disciplines are interested only in violence and not the other dimensions of aggression. In psychological research, aggression is usually conceptualized as behavior that is intended to harm another (see Baron & Richardson, 1994; Coie & Dodge, 1998;

The ESRB’s categorization of violence in this manner coupled with the use of the ESRB ratings in the research create the possibility for maskingof effects. Comparisons of games rated as E (no age restriction recom-mended), which may contain cartoon or fantasy violence, with games rated as M (recommended for those age 17 and older because of mature content), which likely contain graphic violence, may yield different results than would comparisons of M-rated games with games matched on other characteristics (such as high levels of action and rapid rates of pacing) with no violence.

The issues with using the ESRB ratings as an indicator of violent content speak to the larger issues surrounding the definition and distinction of violent acts in video games. Those studies that do not use only the ESRBrat-ing rely on a personal judgment—of the participant, the pilot participants, or the experimenter—to describe the perceived level of violence in the stimulus games. Game violence itself is not well defined in these paradigms: Although it appears that violence requires the target to be animate, studies have inconsistently defined actions taken during the course of a sport’s game play (tack-ling, kicking, boxing) or those “clearly” outside the realm of reality as violent actions. Furthermore, levels and kinds of violence are not well differentiated and are not innately or quantitatively hierarchical (stabbing is not inherently worse than shooting, etc.).

Huesmann & Taylor, 2006; VandenBos, 2007).Violence can be defined as an extreme form ofphysical aggression (see Anderson, 2000) or as the intentional use of physical force or power that either results in, or has a high likelihood ofresulting in, harm (Krug, Dahlberg, Mercy, Zwi, &Lozano, 2002).

Thus, all violence is aggression, but not allaggression is violence. This distinction is important for understanding this research literature, for con-sidering the implications of the research, and forinterpreting popular press accounts of the research and its applicability to societal events.

Definitions of violence in video games

In reviewing this literature, we found that video game violence was not well specified or controlled. Most of the studies relied on either the rating system devised by the Entertainment Software Rating Board (ESRB) or a personal judgment by participants or the experimenters to determine whether a game was violent. The ESRB is an industry-wide self-regulatory body.

Because virtually all games that children play have ratings, the ESRB might appear to be a natural way by which to evaluate or compare them; however, reliance on the ESRB ratings is problematic. These ratings are not based solely on the violence in the game and do not include definitions or descriptions of what is considered to be violence. Ratings are based on considerations such as crude humor; profanity; alcohol, tobacco, and drug use; sexual content or nudity; and gambling. Moreover, the ESRB system uses the term violence, not aggression, and does not differentiate the two. In addition, not all types of violence are handled in the same manner. The ESRB system makes distinctions among violence, cartoon violence, and fantasy violence, based largely on the qualities of the characters involved as well as the outcome of the violence. However, there appears to be no empirical basis for these distinctions.

This definitional problem has undoubtedly colored the research findings ofthis field. Game violence should be better and more uniformly operationalized in order to increase our understanding of the impact of violent video game use. This is an empirical concern that can be addressed through research.

Causality and ethical conduct of research

Although valid methodology for establishing causality, and, indeed, even the definition of causality, are not firmly settled issues (see, e.g., Pearl, 2009), the randomized clinical trial is generally taken to be the ideal standard in many areas of empirical research with human and animal participants. This design is characterized by the random assignment of participants to various experimen-tal conditions and optimally features large samples and controls for various third factors that might have an impact on the causal influence of the target variable. Well-executed and well-replicated randomized clinical trials are gen-erally taken as the only research design from which causality can be uncondi-tionally inferred. APA’s “Reporting Standards for Research in Psychology: Why Do We Need Them? What Might They Be?” provides a comprehensive reviewof this type of experimental paradigm (APA Publications & Communications Board Working Group on Journal Article Reporting Standards, 2008).

However, ethical constraints in exposing participants, especially children and teens, to harmful stimuli, difficulty in controlling exposure due to the widespread nature of modern media, difficulty offering meaningful levels ofexposure in laboratory settings, and the ever-present challenge of obtaining large samples limit the feasibility of randomized clinical trials in this domain.

Given the ethical and pragmatic realities, it is unlikely that it will be pos-sible to conduct definitive studies that can establish causality. This is similarto the limitations on other research addressing violence and abuse as well as other harmful behaviors such as smoking tobacco. Moreover, randomly controlled trials may suffer from limitations such as selection bias. We must therefore ask what we might expect and find useful for inferring causality. Convergence of results across multiple methods, multiple samples, and multi-ple researchers, creating a collective body of scientific inquiry yielding similar results, is an accepted method for inferring causality in behavioral science.

How strong is the evidence for causality?

Themostcommonempiricalfindingofabivariatecross-sectional correlation between violent video game use and aggressive behavior can be misleading about any causal relation, due to possible common association with a thirdvariable or backward causation. Three methods were found across studies to constrain these alternate possibilities. First, some of the studies included covariates that might account for a spurious correlation, such as gender, age, and prior level of aggressiveness. We found that although inclusion ofthese covariates in general lowered the remaining effect size, they did not fully account for the relation between violent video game use and aggressive behavior. We noted that although this empirical strategy is appropriate, itis never conclusive because the possibility always looms of an unmeasured third variable that causes both violent video game use and aggressive behav-ior, rendering the correlation spurious.

The second method used was a laboratory experiment in which individ-uals are randomly assigned to exposure to violent video game use (or not) for a period of time or sessions and then observed for impact on aggres-sive outcomes. This method provides uniform evidence of a causal impact on the aggressive outcomes measured at a magnitude similar to the overall effect size reported previously. Although this method provides the strongest evidence in all of science for the impact of a factor on an outcome, in the current context conclusions from the experimental literature are tempered by the limited ecological validity of the independent and dependent variables. Specifically, because the independent variable is typically a directive by an authoritative adult to engage in violent video game use in a university labora-tory (which differs from self-selected violent video game use in one’s natural environment), the participant might be induced to demonstrate the impactthat the participant infers the researcher desires (the so-called demand characteristic effect on compliance). However, the small dose received inthe laboratory is likely to have a smaller impact than the actual dose received by individuals across their lifetime.

Regarding the dependent variable, the measures typically used in labora-tory experiments are self-reports or directly observed measures of aggression in a simulated or game context (such as delivering hot sauce to an opponent) that have limited generalizability to outcomes of real-world interest. We con-cluded that the laboratory experiments are an important but not conclusive component of the array of empirical evidence.

The third method used was longitudinal inquiry across years of time,in which causal interpretations are constrained by temporal precedence, covariates are measured, the independent variable of violent video game use is measured contemporaneously, and ecologically valid dependent variables are measured over time. This method was used in several more recent studies that found similar effect sizes, as noted previously. The limit of this method is that unmeasured third variables could account for any empirical relation.

No single method or study is conclusive in this field. One method’s lim-its are offset by another method’s strengths. The conclusions we reached are based on the combination of methods used across studies performed in multi-ple countries by multiple disciplines and multiple unique researchers. We note that our strategy of inference based on a combination of studies using com-plementary methods has been well documented in many fields of public health science. On the basis of the body of empirical evidence, we concluded that the impact of exposure to violent video game use on aggressive outcomes is robust.

Applicability to U.S. population

The U.S. population is becoming more racially and ethnically diverse with each passing decade. Census 2000 (U.S. Census Bureau, 2013) and Census 2010 (U.S. Census Bureau, n.d.) attested to that fact. In a national sam-ple, Hispanic and African American youths ages 8–18 were also reported tospend significantly more time playing video games on a typical day than their Caucasian counterparts ( 1:35, 1:35, and 0:56 hours:minutes per day, respec-tively; Rideout et al., 2010).

Other factors

Researchers have begun to explore game characteristics other than violence as an explanation of the link between violent video game use and aggres-sion. Competition, in particular, has been put forth as an alternative reason for aggression (see Adachi & Willoughby, 2011). When gamers compete withone another, an element of that competition can involve aggressive conduct toward another player for the goal of winning. Such behaviors should be less likely to occur when cooperative game play occurs, even when the aggressive content is part of the game, because teamwork requires people to work with one another to win the game. Competition, then, may provide an independent influence on aggressive outcomes after playing aggressive video games. The literature on competition as the underlying causal component of the apparent link between violent game use and aggression is still nascent and is not currently substantial enough to influence, on its own, an objective assessment of the broader violent video game research.

On the basis of our review of the literature directly addressing violent video game use, we concluded that violent video game use has an effect on aggres-sion. This effect is manifested both as an increase in negative outcomes such as aggressive behavior, cognitions, and affect and as a decrease in positive outcomes such as prosocial behavior, empathy, and sensitivity to aggression. Although additional outcomes such as criminal violence, delinquency, and physiological and neurological changes appear in this literature, we did not find enough evidence of sufficient utility to evaluate whether these outcomes are affected by violent video game use. To the extent that other known risk factors of aggression are examined as covariates in this literature, these factors do not account for all of the variance in the link between violent video game use and aggressive outcomes.

No single risk factor consistently leads a person to act aggressively or violently. Rather, it is the accumulation of risk factors that tends to lead toaggressive or violent behavior (Berkowitz, 1993; Eron, Huesmann, Lefkowitz,& Walder, 1974; Ferguson et al., 2013). Each risk factor increases the like-lihood of such negative behavior (Sameroff, Bartko, Baldwin, Baldwin, &Seifer, 1988). The research reviewed here demonstrates that violent video game use is one such risk factor.

Adachi, P. J. C., & Willoughby, T. (2011). The effect of video game competi-tion and violence on aggressive behavior: Which characteristic has the greatest influence? Psychology of Violence, 1, 259–274.

American Psychological Association Publications & Communications Board Working Group on Journal Article Reporting Standards. (2008).Reporting standards for research in psychology: Why do we need them? What might they be? American Psychologist, 63, 839–851. doi:10.1037/0003-066X.63.9.839

Anderson, C. A. (2000). Violence and aggression. In A. E. Kazdin (Ed.), Encyclopedia of psychology (Vol. 8, pp. 162–169). Washington, DC: Author.

Anderson, C. A., Shibuya, A., Ihori, N., Swing, E. L., Bushman, B. J., Sakamoto, A., Rothstein, H. R., & Saleem, M. (2010). Violent video game effects on aggression, empathy, and prosocial behavior in Eastern and Western countries: A meta-analytic review. Psychological Bulletin, 136, 151–173.

Baron, R. A., & Richardson, D. R. (Eds.). (1994). Human aggression: Perspectives in social psychology. New York, NY: Springer.

Berkowitz, L. (1993). Aggression: Its causes, consequences, and control. New York, NY: McGraw-Hill.

Brown v. Entertainment Merchants Association, 564 U.S. 08–1448 (2011).Bushman, B. J. (2013, March). Testimony before the House Subcommittee

onCommerce,Justice, ScienceandRelatedAgencies.Retrieved from http://appropriations.house.gov/uploadedfiles/hhrg-113-ap19- wstate-bushmanb-20130319.pdf

Calvert, S. L. (1999). Children’s journeys through the information age. Boston, MA: McGraw-Hill.

Calvert, S.L. (2015). Children and digital media. In R. Lerner (Series Ed.)
& M. Bornstein & T. Leventhal (Vol. Eds.), Handbook of child psychology and developmental science: Vol. 4. Ecological settings and processes (7th ed., pp. 375–415). Hoboken, NJ: Wiley.

Calvert, S. L., Murray, K., & Conger, E. (2004). Heroic DVD portrayals: What American and Taiwanese adolescents admire and understand. Journal of Applied Developmental Psychology, 25, 699–716.

Cohen, J. (1988). Set correlation and contingency tables. Applied Psychological Measurement, 12, 425–434. doi:10.1177/014662168801200410

Cohen, J. (1992). A power primer. Psychological Bulletin, 112, 155–159. doi:10.1037/0033-2909.112.1.155

Coie, J. D., & Dodge, K. A. (1988). Multiple sources of data on social behav-ior and social status in the school: A cross-age comparison. Child Development, 59, 815–829.

Dodge, K. A., Coie, J. D., & Lynam, D. (2006). Aggression and antisocial behavior in youth. In N. Eisenberg, W. Damon, & R. M. Lerner (Eds.), Handbook of child psychology: Vol. 3. Social, emotional, and per-sonality development (6th ed., pp. 719–788). Hoboken, NJ: Wiley.

Duval, S., & Tweedie, R. (2000). Trim and fill: A simple funnel plot-based method of testing and adjusting for publication bias in meta-analy-sis. Biometrics, 56, 455–463.

Eron, L. D., Huesmann, L. R., Lefkowitz, M. M., & Walder, L. O. (1974). How learning conditions in early childhood—including mass media— relate to aggression in late adolescence. American Journal ofOrthopsychiatry, Vol 44(3), 412–423. doi:10.1111/j.1939-0025.1974.tb00894.x

Federal Bureau of Investigation. (2013). Crime in the United States 2012: Uniform crime reports. Retrieved from https://www.fbi.gov/ about-us/cjis/ucr/crime-in-the-u.s/2012/crime-in-the-u.s.-2012

Ferguson, C. J. (2007a). Evidence for publication bias in video game violence effects literature: A meta-analytic review. Aggression and Violent Behavior, 12, 470–482.

Ferguson, C. J. (2007b). The good, the bad and the ugly: A meta-analytic review of positive and negative effects of violent video games. Psychiatric Quarterly, 78, 309–316. doi:10.1007/s11126-007-9056-9

REFERENCES

17

Ferguson, C. J., Garza, A., Jerabeck, J., Ramos, R., & Galindo, M. (2013). Not worth the fuss after all? Cross-sectional and prospective data on violent video game influences on aggression, visuospatial cogni-tion and mathematics ability in a sample of youth. Journal of Youth and Adolescence, 42, 109–122.

Ferguson, C. J., & Kilburn, J. (2009). The public health risks of media vio-lence: A meta-analytic review. Journal of Pediatrics, 154, 759–763. doi:10.1016/j.jpeds.2008.11.033

Hamby, S., Finkelhor, D., & Turner, H. (2013). Perpetrator and victim gender patterns for 21 forms of youth victimization in the National Survey ofChildren’s Exposure to Violence. Violence and Victims, 28, 915–939.

Hedges,L.V.(1992).Modelingpublicationselectioneffectsinmeta-analysis. Statistical Science,7,246–255.

Hedges, L. V., & Olkin, I. (1984). Nonparametric estimators of effectsize in meta-analysis. Psychological Bulletin, 96, 573–580. doi:10.1037/0033-2909.96.3.573

Herrenkohl, T. I., Maguin, E., Hill, K. G., Hawkins, J. D., Abbott, R. D., &Catalano, R. F. (2000). Developmental risk factors for youth vio-lence. Journal of Adolescent Health, 24, 176–186.

Huesmann, R. L., & Taylor, L. D. (2006). The role of media violence inviolent behavior. Annual Review of Public Health, 27, 393–415. doi:10.1146/annurev.publhealth.26.021304.144640

Kotler,J.A.,&Calvert,S.L.(2003). Children’sandadolescents’exposure todifferent kindsofmediaviolence:Recurringchoicesandrecur-ring themes. In D. Gentile (Ed.), Media violence and children (pp. 171–813). Westport, CT: Praeger.

Krug, E. G., Dahlberg, L. L., Mercy, J. A., Zwi, A. B., & Lozano, R. (2002).World report on violence and health. Geneva, Switzerland: World Health Organization.

Lenhart, A., Kahne, J., Middaugh, E., MacGill, A., Evans, C., & Vitak, J.(2008). Teens, video games and civics. Washington, DC: Pew Internet & American Life Project. Retrieved from http://www. pewinternet.org/files/old-media//Files/Reports/2008/PIP_Teens_ Games_and_Civics_Report_FINAL .pdf.pdf

McGinnis,J.M.,Gootman,J.A.,&Kraak,V.I.(Eds.).(2006). Foodmar-keting to youth: Threat or opportunity? Washington, DC: National Academies Press.

NPD Group. (2011). Kids and gaming, 2011. Port Washington, NY: Author. O’Keefe, B. J., & Zehnder, S. (2004). Understanding media development:

A framework and case study. Journal of Applied Developmental

Psychology, 25, 729–740.
Oxman, A. D. ( 1993). Checklists for review articles. BMJ, 309, 648–651.

Pearl, J. (2009). Causality: Models, reasoning, and inference (2nd ed.). Cambridge, England: Cambridge University Press.

Przybylski, A.K., Rigby, C. S., & Ryan, R. M. (2010). A motivational model ofvideo game engagement. Review of General Psychology, 14, 154–166.

Rideout, V. (2013). Zero to eight: Children’s media use in America 2013. San Francisco, CA: Common Sense Media.

Rideout, V. J., Foehr, U. G., & Roberts, D. F. (2010). Generation M2: Media in the lives of 8–18 year olds. Retrieved from http://kaiserfamilyfoundation.files.wordpress.com/2013/01/8010.pdf

Sameroff, A. J., Bartko, W. T., Baldwin, A., Baldwin, C., & Seifer, R. (1988). Family and social influences on the development of child compe-tence.InM.Lewis&C.Feiring(Eds.), Families,risk, andcompe-tence(pp.161–185).Mahwah,NJ:Erlbaum.

Savage, J., & Yancey, C. (2008). The effects of media violence exposure on criminal aggression: A meta-analysis. Criminal Justice and Behavior, 35, 772–791.

U.S. Census Bureau. (2013). Census 2000 Gateway. Retrieved from https://www.census.gov/main/www/cen2000.html

U.S. Census Bureau. (n.d.). Census 2010. Retrieved from http://www.cen-sus.gov/2010census

VandenBos, G. R. (Ed.). (2007). APA dictionary of psychology. Washington, DC: American Psychological Association.

Wright,J.C.,Huston,S.C.,Ross,R.P.,Calvert,S.L.,Rollandeli,D., Weeks,L.A.,…Potts, R.(1984).Paceandcontinuity oftelevision programs: Effects on children’s attention and comprehension. Developmental Psychology, 20, 653–666.

Zief, S., & Agodini, R. (2012). Supporting policy and program decisions: Recommendations for conducting high quality systematic evi-dence reviews. Washington, DC: Mathematica Policy Research.

18

APPENDIX A
Publications for Systematic Evidence ReviewA1

*Adachi, P. J. C., & Willoughby, T. (2011a). The effect of video game compe-tition and violence on aggressive behavior: Which characteristic has the greatest influence? Psychology of Violence, 1, 259–274. doi:10.1037/a0024908

Adachi, P. J. C., & Willoughby, T. (2011b). The effect of violent video games on aggression: Is it more than just violence? Aggression and Violent Behavior, 16, 55–62.

Adachi, P. J. C., & Willoughby, T. (2013a). Demolishing the competition: The longitudinal link between competitive video games, competitive gambling, and aggression. Journal of Youth and Adolescence, 42, 1090–1104.

Adachi, P. J. C., & Willoughby, T. (2013b). Do video games promote positive youth development? Journal of Adolescent Research, 28, 155–165. Adachi, P. J., & Willoughby, T. (2013c). More than just fun and games: The lon-

gitudinal relationships between strategic video games, self-reported problemsolvingskills,andacademicgrades.Journal ofYouthand Adolescence, 42, 1041–1052.

Allahverdipour, H., Bazargan, M., Farhadinasab, A., & Moeini, B. (2010).Correlates of video games playing among adolescents in an Islamic country. BMC Public Health, 10(1), 286.

Anderson, C. A., & Carnagey, N. L. (2009). Causal effects of violent sports video games on aggression: Is it competitiveness or violent content? Journal of Experimental Social Psychology, 45, 731–739.

Anderson, C. A., & Prot, S. (2011). Effects of playing violent video games. In M. A Paludi (Ed.), The psychology of teen violence and victim-ization: Vol. 2. Prevention strategies for families and schools (pp. 41–70). Santa Barbara, CA: Praeger/ABC-CLIO.

*†Arriaga, P., Monteiro, M. B., & Esteves, F. (2011). Effects of playing violent computer games on emotional desensitization and aggressive behavior. Journal of Applied Social Psychology, 41, 1900–1925.

A1Asterisks (*) denote articles coded for study characteristics. Daggers (†) denote articles included in the systematic evidence review.

Ashworth, L., Pyle, M., & Pancer, E. (2010). The role of dominance in the appeal of violent media depictions. Journal of Advertising, 39,121–134.

*Bailey, K., West, R., & Anderson, C. A. (2011). The association between chronic exposure to video game violence and affective picture processing: An ERP study. Cognitive, Affective & Behavioral Neuroscience, 11, 259–276. doi:10.3758/s13415-011-0029-y

Ballard, M., Visser, K., & Jocoy, K. (2012). Social context and video game play: Impact on cardiovascular and affective responses. Mass Communication and Society, 15, 875–898.

Barlett, C. P., Anderson, C. A., & Swing, E. L. (2009). Video game effects— Confirmed, suspected, and speculative: A review of the evidence. Simulation and Gaming, 40, 377–403.

Barlett, C. P., Vowels, C. L., Shanteau, J., Crow, J., & Miller, T. (2009).The effect of violent and non-violent computer games on cognitive performance.ComputersinHumanBehavior,25,96–102.

*Bastian, B., Jetten, J., & Radke, H. R. M. (2012). Cyber-dehumanization: Violent video game play diminishes our humanity. Journal ofExperimental Social Psychology, 48, 486–491.

Beck, V. S., Boys, S., Rose, C., & Beck, E. (2012). Violence against women in video games: A prequel or sequel to rape myth acceptance?

Journal of Interpersonal Violence, 27, 3016–3031.
Becker-Olsen, K. L., & Norberg, P. A. (2010). Caution, animated violence:

Assessing the efficacy of violent video game ratings. Journal of

Advertising, 39, 83–94.
The behavioural effects of video games: Good game? (2009, May 28).

The Economist. Retrieved from http://www.economist.com/

node/13726738
Bennerstedt, U., Ivarsson, J., & Linderoth, J. (2012). How gamers manage

aggression: Situating skills in collaborative computer games. International Journal of Computer-Supported Collaborative Learning, 7, 43–61.

19

Beullens, K., Roe, K., & Van den Bulck, J. (2011). Excellent gamer, excel-lent driver? The impact of adolescents’ video game playing on driving behavior: A two-wave panel study. Accident Analysis and Prevention, 43, 58–65.

*†Bluemke, M., Friedrich, M., & Zumbach, J. (2010). The influence of violent and nonviolent computer games on implicit measures of aggressive-ness. Aggressive Behavior, 36, 1–13.

Bolton, A. G. (2010). Individual differences in the effects of playing violent video games: Specific play rehearsals and changes in aggression. Dissertation Abstracts International: Section B. Sciences and Engineering, 70(7), 4533.

Bond, D. (2011). The effects of violent video games on aggressive behav-ior and the relationship to school shootings (Unpublished doctoral dissertation). BondUniversity,Robina,Queensland,Australia.

Boot, W. R., Champion, M., Blakely, D. P., Wright, T., Souders, D. J., &Charness, N. (2013). Video games as a means to reduce age- related cognitive decline: Attitudes, compliance, and effectiveness. Frontiers in Psychology, 4, 1–9.

Bösche, W. (2009). Violent content enhances video game perfor-mance. Journal of Media Psychology: Theories, Methods, and Applications,21,145–150.

*†Bösche, W. (2010). Violent video games prime both aggressive and positive cognitions. Journal of Media Psychology: Theories, Methods, and Applications, 22, 139–146.

Bösche, W. (2012). Application of the signal detection theory to the cogni-tive processing of aggressive stimuli after playing a violent video game: Response bias or enhanced sensitivity? In A. M. Columbus (Ed.), Advances in psychology research (Vol. 91, pp. 135–142). Hauppauge, NY: Nova Science.

*Bowen, H. J., & Spaniol, J. (2011). Chronic exposure to violent video games is not associated with alterations of emotional memory. Applied Cognitive Psychology, 25, 906–916.

Boxer, P., Huesmann, L. R., Bushman, B. J., O’Brien, M., & Moceri, D.(2009). The role of violent media preference in cumulative develop-mental risk for violence and general aggression. Journal of Youth and Adolescence, 38, 417–428.

Brockmyer, J. H., Fox, C. M., Curtiss, K. A., McBroom, E., Burkhart, K. M., &Pidruzny, J. N. (2009). The development of the Game Engagement Questionnaire: A measure of engagement in video game-playing.

Journal of Experimental Social Psychology, 45, 624–634.
Burgess, M. R., Dill, K. E., Stermer, S., Burgess, S. R., & Brown, B. P. (2011).

Playing with prejudice: The prevalence and consequences of racial stereotypes in video games. Media Psychology, 14, 89–311.

Busching, R., Gentile, D. A., Krahé, B., Möller, I., Khoo, A., Walsh, D. A.,& Anderson, C. A. (2013). Testing the reliability and validity ofdifferent measures of violent video game use in the United States, Singapore, and Germany. Psychology of Popular Media Culture. Advance online publication. doi:10.1037/ppm0000004

*†Bushman, B. J., & Gibson, B. (2011). Violent video games cause an increase in aggression long after the game has been turned off. Social Psychological & Personality Science, 2, 29–32.

Bushman, B. J., & Whitaker, J. L. (2010). Like a magnet: Catharsis beliefs attract angry people to violent video games. Psychological Science,21, 790–792.

*Charles, E. P., Baker, C. M., Hartman, K., Easton, B. P., & Kreuzberger, C. (2013). Motion capture controls negate the violent video-game effect.ComputersinHumanBehavior,29,2519–2523.

Chory, R. M., & Goodboy, A. K. (2011). Is basic personality related to violent and non-violent video game play and preferences? Cyberpsychology, Behavior and Social Networking, 14, 191–198.

*Chou, Y. H., Yang, B. H., Hsu, J. W., Wang, S. J., Lin, C. L., Huang, K. L.,& Lee, S. M. (2013). Effects of video game playing on cerebral blood flow in young adults: A SPECT study. Psychiatry Research: Neuroimaging, 212,65–72.

Commonwealth of Australia. (2010). Literature review on the impact of playing violent video games on aggression. Retrieved from http://www.ag.gov.au/cca

Coyne, S. M., Padilla-Walker, L. M., & Howard, E. (2013). Emerging in a dig- ital world: A decade review of media use, effects, and gratifications in emerging adulthood. Emerging Adulthood, 1, 125–137.

Coyne, S. M., Padilla-Walker, L. M., Stockdale, L., & Day, R. D. (2011).
Game on … girls: Associations between co-playing video games and adolescent behavioral and family outcomes. Journal of Adolescent Health, 49, 160–165.

*†DeLisi, M., Vaughn, M. G., Gentile, D. A., Anderson, C. A., & Shook, J. J. (2013). Violent video games, delinquency, and youth violence: New evidence. Youth Violence and Juvenile Justice, 11, 132–142.

*Denzler, M., Häfner, M., & Förster, J. (2011). He just wants to play: How goals determine the influence of violent computer games on aggres-sion. Personality and Social Psychology Bulletin, 37, 1644–1654.

*†Devilly, G. J., Callahan, P., & Armitage, G. (2012). The effect of violent vid-eogame playtime on anger. Australian Psychologist, 47, 98–107. Elliott, L., Ream, G., McGinsky, E., & Dunlap, E. (2012). The contribution of game genre and other use patterns to problem video game play

among adult video gamers. International Journal of Mental Health and Addiction, 10, 948–969.

20

*Engelhardt, C. R., Bartholow, B. D., Kerr, G. T., & Bushman, B. J. (2011).This is your brain on violent video games: Neural desensitization to violence predicts increased aggression following violent video game exposure. Journal of Experimental Social Psychology, 47, 1033–1036.

Ewoldsen, D. R., Eno, C. A., Okdie, B. M., Velez, J. A., Guadagno, R. E., &DeCoster, J. (2012). Effect of playing violent video games coop-eratively or competitively on subsequent cooperative behavior. Cyberpsychology, Behavior and Social Networking, 15, 277–280.

Farman, J. (2010). Hypermediating the game interface: The alienation effect in violent videogames and the problem of serious play. Communication Quarterly, 58, 96–109.

Ferguson, C. J. (2010). Blazing angels or resident evil? Can violent video games be a force for good? Review of General Psychology, 14,68–81.

*Ferguson, C. J. (2011a). The influence of television and video game use
on attention and school problems: A multivariate analysis withother risk factors controlled. Journal of Psychiatric Research, 45, 808–813.

*Ferguson, C. J. (2011b). Video games and youth violence: A prospective analysis in adolescents. Journal of Youth and Adolescence, 40,377–391.

Ferguson, C. J., & Dyck, D. (2012). Paradigm change in aggression research: The time has come to retire the general aggression model. Aggression and Violent Behavior, 17, 220–228.

*Ferguson,C.J.,&Garza,A.(2011).Callof(civic) duty:Actiongamesand civic behavior in a large sample of youth. Computers in Human Behavior, 27, 770–775.

*†Ferguson, C. J., Garza, A., Jerabeck, J., Ramos, R., & Galindo, M. (2013). Not worth the fuss after all? Cross-sectional and prospective data on violent video game influences on aggression, visuospatial cogni-tion and mathematics ability in a sample of youth. Journal of Youth and Adolescence, 42, 109–122.

Ferguson, C. J., & Olson, C. K. (2013a). Friends, fun, frustration and fantasy: Child motivations for video game play. Motivation and Emotion, 37, 154–164.

*Ferguson, C. J., & Olson, C. K. (2013b). Violent video game use among “vulnerable” populations: The impact of violent video games on

delinquency and bullying among children with clinically elevated depression or attention deficit symptoms. Journal of Youth and Adolescence, 43, 127–136.

*Ferguson, C. J., Olson, C. K., Kutner, L. A., & Warner, D. E. (2014). Violent video games, catharsis seeking, bullying, and delinquency: A multi-variate analysis of effects. Crime & Delinquency, 60, 764–784.

*Ferguson, C. J., & Rueda, S. M. (2010). The Hitman study: Violent video game exposure effects on aggressive behavior, hostile feelings, and depression. European Psychologist, 15, 99–108.

*Ferguson, C. J., San Miguel, C., Garza, A., & Jerabeck, J. M. (2012). A longitudinal test of video game violence influences on dating and aggression: A 3-year longitudinal study of adolescents. Journal ofPsychiatric Research, 46, 141–146.

*Ferguson, C. J., San Miguel, C., & Hartley, R. D. (2009). A multivariate analysis of youth violence and aggression: The influence of family, peers, depression, and media violence. Journal of Pediatrics, 155, 904–908.

Fischer, J., Aydin, N., Kastenmüller, A., Frey, D., & Fischer, P. (2012). The delinquent media effect: Delinquency-reinforcing video games increase players’ attitudinal and behavioral inclination toward delinquent behavior. Psychology of Popular Media Culture, 1,201–205.

Fischer, P., Kastenmüller, A., & Greitemeyer, T. (2010). Media violence and the self: The impact of personalized gaming characters in aggres-sive video games on aggressive behavior. Journal of Experimental Social Psychology, 46, 192–195.

*Fraser, A. M., Padilla-Walker, L. M., Coyne, S. M., Nelson, L. J., & Stockdale, L. A. (2012). Associations between violent video gaming, empathic concern,andprosocialbehaviortowardstrangers,friends,and family members. Journal of Youth and Adolescence, 41, 636–649.

*†Gabbiadini, A., Andrighetto, L., & Volpato, C. (2012). Brief report: Does exposure to violent video games increase moral disengagement among adolescents? Journal of Adolescence, 35, 1403–1406.

Gentile, D. A., Anderson, C. A., & Olson, C. K. (2010). Do video games lead to violence? In B. Slife (Ed.), Taking sides: Clashing views on psychological issues (16th ed., pp. 327–341). New York, NY: McGraw-Hill.

Gentile, D. A., & Bushman, B. J. (2012). Reassessing media violence effects using a risk and resilience approach to understanding aggression. Psychology of Popular Media Culture, 1, 138–151.

Gentile, D. A., Coyne, S., & Walsh, D. A. (2011). Media violence, physical aggression, and relational aggression in school age children:
A short-term longitudinal study. Aggressive Behavior, 37, 193–206.

Gentile, D. A., Mathieson, L. C., & Crick, N. R. (2011). Media violence asso-ciations with the form and function of aggression among elementary school children. Social Development, 20, 213–232.

21

Gentile, D. A., Swing, E. L., Lim, C. G., & Khoo, A. (2012). Video game play-ing, attention problems, and impulsiveness: Evidence of bidirec-tional causality. Psychology of Popular Media Culture, 1, 62–70.

*Glock, S., & Kneer, J. (2009). The impact of knowledge about violent digital games on the activation of aggression-related concepts. Journal ofMedia Psychology, 21, 151–160.

*Gollwitzer, M., & Melzer, A. (2012). Macbeth and the joystick: Evidence for moral cleansing after playing a violent video game. Journal ofExperimental Social Psychology, 48, 1356–1360.

Green, C. S., Sugarman, M. A., Medford, K., Klobusicky, E., & Bavelier, D. (2012). The effect of action video game experience on task-switching. Computers in Human Behavior, 28, 984–994.

Greitemeyer, T. (2013). Effects of playing video games on perceptions ofhumanity. Journal of Social Psychology, 153, 499–514. doi:10.1080 /00224545.2013.768593

*Greitemeyer, T., & McLatchie, N. (2011). Denying humanness to others: A newly discovered mechanism by which violent video games increase aggressive behavior. Psychological Science, 22, 659–665.

Greitemeyer, T., & Osswald, S. (2011). Playing prosocial video games increases the accessibility of prosocial thoughts. Journal of Social Psychology, 151, 121–128.

*Greitemeyer, T., Traut-Mattausch, E., & Osswald, S. (2012). How toameliorate negative effects of violent video games on cooperation: Play it cooperatively in a team. Computers in Human Behavior, 28, 1465–1470.

Gunter, W. D., & Daly, K. (2012). Causal or spurious: Using propensity score matching to detangle the relationship between violent video games and violent behavior. Computers in Human Behavior, 28, 1348–1355.

Guo, X., Zheng, L., Wang, H., Zhu, L., Li, J., Wang, Q., & Yang, Z. (2013). Exposure to violence reduces empathetic responses to other’s pain. Brain and Cognition, 82, 187–191.

Happ, C., Melzer, A., & Steffgen, G. (2011). Bringing empathy into play: On the effects of empathy in violent and nonviolent video games. In J. Anacleto et al. (Eds.), Entertainment computing–ICEC 2011 (pp. 371–374). Berlin, Germany: Springer.

*†Happ, C., Melzer, A., & Steffgen, G. (2013). Superman v. BAD man? The effects of empathy and game character in violent video games. Cyberpsychology, Behavior and Social Networking, 16, 774–778.

*Hartmann, T., Toz, E., & Brandon, M. (2010). Just a game? Unjustified virtual violence produces guilt in empathetic players. Media Psychology, 13,339–363.

*†Hartmann, T., & Vorderer, P. (2010). It’s okay to shoot a character: Moral disengagement in violent video games. Journal of Communication, 60, 94–119.

*Hasan, Y., Bègue, L., & Bushman, B. J. (2012). Viewing the world through “blood-red tinted glasses”: The hostile expectation bias mediates the link between violent video game exposure and aggression. Journal

of Experimental Social Psychology, 48, 953–956.
*†Hasan, Y., Bègue, L., & Bushman, B. J. (2013). Violent video games stress people out and make them more aggressive. Aggressive Behavior,

39, 64–70.
*†Hasan, Y., Bègue, L., Scharkow, M., & Bushman, B. J. (2013). The more you

play, the more aggressive you become: A long-term experimental study of cumulative violent video game effects on hostile expec-tations and aggressive behavior. Journal of Experimental Social Psychology, 49, 224–227.

*Hastings, E. C., Karas, T. L., Winsler, A., Way, E., Madigan, A., & Tyler, S.(2009). Young children’s video/computer game use: Relations withschool performance and behavior. Issues in Mental Health Nursing, 30, 638–649.

Hellström, C., Nilsson, K., Leppert, J., & Åslund, C. (2012). Influences of motives to play and time spent gaming on the negative conse-quences of adolescent online computer gaming. Computers inHuman Behavior, 28, 1379–1387.

Hofferth, S. L. (2010). Home media and children’s achievement and behav-ior. Child Development, 81, 1598–1619.

*Hollingdale, J., & Greitemeyer, T. (2013). The changing face of aggression: The effect of personalized avatars in a violent video game on levels of aggressive behavior. Journal of Applied Social Psychology, 43, 1862–1868.

*Holtz, P., & Appel, M. (2011). Internet use and video gaming predict problem behavior in early adolescence. Journal of Adolescence, 34, 49–58.

Homer, B. D., Hayward, E. O., Frye, J., & Plass, J. L. (2012). Gender and player characteristics in video game play of preadolescents. Computers in Human Behavior, 28, 1782–1789.

Huesmann, L. R. (2010). Nailing the coffin shut on doubts that violent video games stimulate aggression: Comment on Anderson et al. (2010).Psychological Bulletin, 136,179–181.

Huesmann, L. R., Dubow, E. F., & Yang, G. (2013). Why it is hard to believe that media violence causes aggression. In K. E. Dill (Ed.), The Oxford handbook of media psychology (pp. 159–171). Oxford, England: Oxford University Press.

22

*Hummer, T. A., Wang, Y., Kronenberger, W. G., Mosier, K. M., Kalnin, A. J., Dunn, D. W., & Mathews, V. P. (2010). Short-term violent video game play by adolescents alters prefrontal activity during cognitive inhibition. Media Psychology, 13, 136–154.

Janssen, I., Boyce, W. F., & Pickett, W. (2012). Screen time and physical violence in 10 to 16-year-old Canadian youth. International Journal of Public Health, 57, 325–331.

Jensen, J. D., Weaver, A. J., Ivic, R., & Imboden, K. (2011). Developing a brief sensation seeking scale for children: Establishing concurrent validity with video game use and rule-breaking behavior. Media Psychology,14,71–95.

*†Jeong, E. J., Biocca, F. A., & Bohil, C. J. (2012). Sensory realism and medi-atedaggressioninvideogames.ComputersinHumanBehavior,28, 1840–1848.

Jeong, E. J., Bohil, C. J., & Biocca, F. A. (2011). Brand logo placements inviolentgames:Effectsofviolencecuesonmemoryandattitudethrough arousal and presence. Journal of Advertising, 40, 59–72.

*Jerabeck, J. M., & Ferguson, C. J. (2013). The influence of solitary and cooperative violent video game play on aggressive and prosocial behavior. Computers in Human Behavior, 29, 2573–2578.

*†Jin, S.-A. A. (2011). “My avatar behaves well and this feels right”: Ideal and ought selves in video gaming. Social Behavior and Personality, 39,1175–1182.

Kalnin, A. J., Edwards, C. R., Wang, Y., Kronenberger, W. G., Hummer, T. A., Mosier, K. M., … Mathews, V. P. (2011). The interacting role of media violence exposure and aggressive–disruptive behavior in adoles-cent brain activation during an emotional Stroop task. Psychiatry Research: Neuroimaging, 192, 12–19.

King, D. L., Delfabbro, P. H., & Griffiths, M. D. (2013). Trajectories of prob-lem video gaming among adult regular gamers: An 18-month longi-tudinal study. Cyberpsychology, Behavior and Social Networking, 16, 72–76.

Klasen, M., Zvyagintsev, M., Schwenzer, M., Mathiak, K. A., Sarkheil, P., Weber, R., & Mathiak, K. (2013). Quetiapine modulates functional connectivity in brain aggression networks. Neuroimage, 75, 20–26.

Kneer, J., Glock, S., Beskes, S., & Bente, G. (2012). Are digital games perceived as fun or danger? Supporting and suppressing different game-related concepts. Cyberpsychology, Behavior and Social Networking, 15, 604–609.

Kollstedt, K. J., & Sterling, M. I. (2009). The effect of graphical quality on aggression in violent video games. Unpublished manuscript, Hanover College.

Krahé, B., Busching, R., & Möller, I. (2012). Media violence use and aggres-sion among German adolescents: Associations and trajectories ofchange in a three-wave longitudinal study. Psychology of Popular Media Culture, 1, 152–166.

Krahé, B., & Möller, I. (2010). Longitudinal effects of media violence on aggression and empathy among German adolescents. Journal ofApplied Developmental Psychology, 31, 401–409.

Krahé, B., & Möller, I. (2011). Links between self-reported media violence exposure and teacher ratings of aggression and prosocial behavior among German adolescents. Journal of Adolescence, 34, 279–287.

*†Krcmar,M.,&Farrar,K.(2009). Retaliatoryaggressionandthe effects of point of view and blood in violent video games. Mass Communication&Society, 12,115–138.

*†Krcmar,M.,&Lachlan,K.(2009). Aggressiveoutcomesandvideogame play: The role of length of play and the mechanisms at work. Media Psychology, 12,249–267.

*Lang, A., Bradley, S. D., Schneider, E. F., Kim, S. C., & Mayell, S. (2012). Killing is positive! Journal of Media Psychology: Theories, Methods, and Applications, 24, 154–166.

Lee, K. M., Peng, W., & Klein, J. (2010). Will the experience of playing a violent role in a video game influence people’s judgments of violent crimes? Computers in Human Behavior, 26, 1019–1023.

*Lemmens, J. S., Valkenburg, P. M., & Peter, J. (2011). The effects ofpathological gaming on aggressive behavior. Journal of Youth and Adolescence, 40, 38–47.

Levermore, M. A., & Salisbury, G. L. (2009). The relationship between virtual and actual aggression: Youth exposure to violent media. Forensic Examiner, 18, 32–42.

Lin, S. F. (2010). Gender differences and the effect of contextual features on game enjoyment and responses. Cyberpsychology, Behavior and Social Networking, 13, 533–537.

Lin, J. H. (2012). The moderating role of the media interactivity on the relationship between video game violence and aggression and the mediating role of self-concept. Dissertation Abstracts International: Section A. Humanities and Social Sciences, 72(8), 2642.

*†Lin, J. H. (2013a). Do video games exert stronger effects on aggression than film? The role of media interactivity and identification on the association of violent content and aggressive outcomes. Computers in Human Behavior, 29, 535–543.

*†Lin, J. H. (2013b). Identification matters: A moderated mediation model of media interactivity, character identification, and video game vio-lence on aggression. Journal of Communication, 63, 682–702.

23

Lyons, E. J., Tate, D. F., Ward, D. S., Bowling, J. M., Ribisl, K. M., &Kalyararaman, S. (2011). Energy expenditure and enjoyment during video game play: Differences by game type. Medicine and Science in Sports and Exercise, 43, 1987–1993.

*†Maass, A., Kollhörster, K., Riediger, A., MacDonald, V., & Lohaus, A. (2011).Effects of violent and non-violent computer game content on mem-ory performance in adolescents. European Journal of Psychology of Education, 26, 339–353.

Markey, P. M., & Markey, C. N. (2010). Vulnerability to violent video games: A review and integration of personality research. Review of General Psychology, 14, 82–91.

*Markey, P. M., & Scherer, K. (2009). An examination of psychoticism and motion capture controls as moderators of the effects of violent video games. Computers in Human Behavior, 25, 407–411.

*Mathiak, K. A., Klasen, M., Weber, R., Ackermann, H., Shergill, S. S., &Mathiak, K. (2011). Reward system and temporal pole contributions to affective evaluation during a first person shooter video game. BMC Neuroscience, 12, 66.

McCreery, M. P., Krach, S. K., Schrader, P. G., & Boone, R. (2012). Defining the virtual self: Personality, behavior, and the psychology of embod-iment. Computers in Human Behavior, 28, 976–983.

Melzer, A., Bushman, B. J., & Hofmann, U. G. (2009). When items become victims: Brand memory in violent and nonviolent games. In S. M. Stevens & S. Saldamarco (Eds.), Entertainment computing—ICEC 2008 (pp. 11–22). Berlin, Germany: Springer.

Melzer, A., Derks, I., Heydekorn, J., & Steffgen, G. (2010). Click or strike:Realistic versus standard game controls in violent video games and their effects on aggression. In H. S. Yang, R. Malaka, J. Hoshino,& J. J. Han (Eds.), Entertainment computing—ICEC 2010 (pp. 171–182).Berlin, Germany: Springer.

Mentzoni, R. A., Brunborg, G. S., Molde, H., Myrseth, H., Skouverøe, K. J. M., Hetland, J., & Pallesen, S. (2011). Problematic video game use: Estimated prevalence and associations with mental and physical health. Cyberpsychology, Behavior and Social Networking, 14,591–596.

*†Moller, I., & Krahé, B. (2009). Exposure to violent video games and aggres-sion in German adolescents: A longitudinal analysis. Aggressive Behavior, 35, 75–89.

Moller, I., Krahé, B., Busching, R., & Krause, C. (2012). Efficacy of an intervention to reduce the use of media violence and aggression: An experimental evaluation with adolescents in Germany. Journal ofYouth and Adolescence, 41, 105–120.

*Montag, C., Weber, B., Trautner, P., Newport, B., Markett, S., Walter, N. T., & Reuter, M. (2012). Does excessive play of violent first-per-son-shooter-video-games dampen brain activity in response toemotional stimuli? Biological Psychology, 89, 107–111.

Murray, J. P. (2012). Children and media violence: Behavioural and neuro-logical effects of viewing violence. In W. Warburton & D. Braunstein

(Eds.), Growing up fast and furious: Reviewing the impacts ofviolent and sexualised media on children (pp. 34–55). Annandale, New South Wales, Australia: Federation Press.

*†Nije Bijvank, M., Konijn, E. A., & Bushman, B. J. (2012). “We don’t need no education”: Video game preferences, video game motivations, and aggressiveness among adolescent boys of different educational ability levels. Journal of Adolescence, 35, 153–162.

Oxford, J., Ponzi, D., & Geary, D. C. (2010). Hormonal responses differwhen playing violent video games against an ingroup and outgroup.Evolution and Human Behavior, 31, 201–209.

Przybylski, A. K., Ryan, R. M., & Rigby, C. (2009). The motivating role of violence in video games. Personality and Social Psychology Bulletin, 35, 243–259.

Puri, K., & Pugliese, R. (2012). Sex, lies, and video games: Moral panics or uses and gratifications. Bulletin of Science, Technology & Society, 32, 345–352.

*†Regenbogen, C., Herrmann, M., & Fehr, T. (2010). The neural processing ofvoluntary completed, real and virtual violent and nonviolent com-puter game scenarios displaying predefined actions in gamers and nongamers. Social Neuroscience, 5, 221–240.

Rehbein, F., & Kleimann, M. (2010). Prevalence and risk factors of video game dependency in adolescence: Results of a German nationwide study. Cyberpsychology, Behavior and Social Networking, 13,269–277.

Rothmund, T., Gollwitzer, M., & Klimmt, C. (2011). Of virtual victims and victimized virtues: Differential effects of experienced aggression in video games on social cooperation. Personality and Social Psychology Bulletin, 37, 107–119.

Saleem, M., & Anderson, C. A. (2013). Arabs as terrorists: Effects of stereo-types within violent contexts on attitudes, perceptions, and affect. Psychology of Violence, 3, 84–99.

*†Saleem, M., Anderson, C. A., & Gentile, D. A. (2012a). Effects of prosocial, neutral, and violent video games on children’s helpful and hurtfulbehaviors. Aggressive Behavior, 38, 281–287.

*†Saleem, M., Anderson, C. A., & Gentile, D. A. (2012b). Effects of proso-cial, neutral, and violent video games on college students’ affect. Aggressive Behavior, 38, 263–271.

24

*Schmierbach, M. (2010). “Killing spree”: Exploring the connection between competitive game play and aggressive cognition. Communication Research, 37, 256–274.

Seo, M., Kang, H. S., & Chae, S. M. (2012). Emotional competence and online game use in adolescents. Computers Informatics Nursing, 30, 640–646.

Sestir, M. A., & Bartholow, B. D. (2010). Violent and nonviolent video games produce opposing effects on aggressive and prosocial outcomes. Journal of Experimental Social Psychology, 46, 934–942.

*†Shafer, D. (2012). Causes of state hostility and enjoyment in player versus player and player versus environment video games. Journal ofCommunication, 62, 719–737.

Strenziok, M., Krueger, F., Deshpande, G., Lenroot, R. K., van der Meer, E.,& Grafman, J. (2011). Fronto-parietal regulation of media violence exposure in adolescents: A multi-method study. Social Cognitive and Affective Neuroscience, 6, 537–547.

Sultanbayeva, L., Shyryn, U., Minina, N., Zhanat, B., & Uaidullakyzy, E. (2013). The influence of computer games on children’s aggression in adolescence. Procedia: Social and Behavioral Sciences, 82, 933–941.

Surette, R. (2012). Cause or catalyst: The interaction of real world and media crime models. American Journal of Criminal Justice, 38,392–409. doi: 10.1007/s12103-012-9177-z

Swing, E. L., Gentile, D. A., Anderson, C. A., & Walsh, D. A. (2010).Television and video game exposure and the development of atten-tion problems. Pediatrics, 126, 214–221.

*Tear, M. J., & Nielsen, M. (2013). Failure to demonstrate that playing violent video games diminishes prosocial behavior. PloS One, 8,e68382.

*Teng, S. K. Z., Chong, G. Y. M., Siew, A. S. C., & Skoric, M. M. (2011). Grand Theft Auto IV comes to Singapore: Effects of repeated exposure toviolent video games on aggression. Cyberpsychology, Behavior and Social Networking, 14, 597–602.

*Thomas, K. D., & Levant, R. F. (2012). Does the endorsement of traditional masculinity ideology moderate the relationship between exposure to violent video games and aggression? Journal of Men’s Studies, 20, 47–56.

Tucker, P. (2009). Video games and behavioral modification. Futurist, 43(1), 8–9.

*Valadez, J. J., & Ferguson, C. J. (2012). Just a game after all: Violent video game exposure and time spent playing: Effects on hostile feelings, depression, and visuospatial cognition. Computers in Human Behavior, 28, 608–616.

*†Von Salisch, M., Vogelgesang, J., Kristen, A., & Oppl, C. (2011). Preference for violent electronic games and aggressive behavior among chil-dren: The beginning of the downward spiral? Media Psychology, 14,233–258.

Wang, C. C., & Yang, M. (2009). Violent game acceptance: The influences of aggression tendency, thrill seeking, and perceived risk. Journal of CyberTherapy and Rehabilitation, 2, 151–158.

*†Wang, Y., Mathews, V. P., Kalnin, A. J., Mosier, K. M., Dunn, D. W., Saykin, A. J., & Kronenberger, W. G. (2009). Short term exposure to a violent video game induces changes in frontolimbic circuitry in adolescents.

Brain Imaging and Behavior, 3, 38–50.
Ward, M. R. (2010). Video games and adolescent fighting. Journal of Law

and Economics, 53, 611–628.
Ward, M. R. (2011). Video games and crime. Contemporary Economic Policy,

29, 261–273.
Weaver,A.J.(2011).Ameta-analytical reviewofselectiveexposureto

and the enjoyment of media violence. Journal of Broadcasting &

Electronic Media, 55, 232–250.
Weaver, A. J., Jensen, J. D., Martins, N., Hurley, R. J., & Wilson, B. J.

(2011). Liking violence and action: An examination of gender differences in children’s processing of animated content. Media Psychology, 14, 49–70.

Weis, R., & Cerankosky, B. C. (2010). Effects of video-game ownership on young boys’ academic and behavioral functioning: A randomized, controlled study. Psychological Science, 21, 463–470.

West, G. L., Al-Aidroos, N., & Pratt, J. (2013). Action video game experience affects oculomotor performance. Acta Psychologica, 142, 38–42.

Whitaker, J. L., & Bushman, B. J. (2012). “Boom, headshot!”: Effect of video game play and controller type on firing aim and accu-racy. Communication Research. Advance online publication.doi:10.1177/0093650212446622.

*†Williams, K. D. (2009). The effects of frustration, violence, and trait hos-tility after playing a video game. Mass Communication and Society,12, 291–310.

*†Williams, K. D. (2011). The effects of homophily, identification, and violent video games on players. Mass Communication and Society, 14,3–24.

Willoughby, T., Adachi, P. J. C., & Good, M. (2012). A longitudinal study ofthe association between violent video game play and aggression among adolescents. Developmental Psychology, 48, 1044–1057.

Wirth, W., Ryffel, F., von Pape, T., & Karnowski, V. (2013). The development of video game enjoyment in a role playing game. Cyberpsychology, Behavior and Social Networks, 16, 260–264.

25

Yağci, E., & Çağlar, M. (2010). How the use of computer types and frequency affects adolescences towards anger and aggression. Turkish Online Journal of Educational Technology, 9, 89–97.

Yoo, S.-C., & Peña, J. (2011). Do violent video games impair the effective-ness of in-game advertisements? The impact of gaming environ-ment on brand recall, brand attitude, and purchase intention. Cyberpsychology, Behavior and Social Networking, 14, 439–446.

*Zhen, S., Xie, H., Zhang, W., Wang, S., & Li, D. (2011). Exposure to violent computer games and Chinese adolescents’ physical aggression: The role of beliefs about aggression, hostile expectations, and empathy. Computers in Human Behavior, 27, 1675–1687.

26

Age
Grade
Gender
Number of participants
Country of origin of study
Ethnicity, race, or origin of participants Socioeconomic status

Research design
– Experimental or observational study
– Cross-sectional or longitudinal
Delay between exposure and testing
– Present or not
– Analyzed or not
Analytic approach
– Group means comparison, correlational,

modeling, other
Summarystatistics available
Amount of exposure to violent video games- Time of play
– Number of play incidents
Measure of intensity of violence in violent video game
– Entertainment Software Rating Board

rating available
– Participant report – Rater report

Measure of intensity of violence incomparison game
– Is there a comparison game?
– Entertainment Software Rating Board

rating available
– Participant report
– Rater reportOutcomes
– Aggressive behaviors

– Experimental proxy
– Physical aggression
– Verbal aggression
– Relational aggression
– General or composite aggression

– Aggressive cognitions- Aggressive affect -Physiologicalmeasures- Neurological measures- Prosocial behaviors

– Reduced empathy or desensitization- Delinquency
– Criminal violence
– Clinical symptomatology

– Other

Other game characteristics
– Interactivity
– Perspective (first person or third person)
– Cooperation or collaboration
– Competition
– Realism
Environmental risk factors for aggression
– Family violence or abuse
– Peer violence
– Social reputation (peer or teacher nomination)- Neighborhood violence
– Learning disability
– IQ
– Low academic achievement
– Foster care
– Drug use
-Teenparent
– Parental divorce
– Low parental involvement or monitoring Deception detection
Participant source
Participant payment
Note/other

APPENDIX B
Characteristics CodedintheSystematicEvidenceReview

The studies included in the systematic evidence review were coded for the following characteristics:

27