We conducted preregistered replications of 28 classic and contemporary published findings, with protocols that were peer reviewed in advance, to examine variation in effect magnitudes across samples and settings. Each protocol was administered to approximately half of 125 samples that comprised 15,305 participants from 36 countries and territories. Using the conventional criterion of statistical significance ( p < .05), we found that 15 (54%) of the replications provided evidence of a statistically significant effect in the same direction as the original finding. With a strict significance criterion ( p < .0001), 14 (50%) of the replications still provided such evidence, a reflection of the extremely high-powered design. Seven (25%) of the replications yielded effect sizes larger than the original ones, and 21 (75%) yielded effect sizes smaller than the original ones. The median comparable Cohen’s ds were 0.60 for the original findings and 0.15 for the replications. The effect sizes were small (< 0.20) in 16 of the replications (57%), and 9 effects (32%) were in the direction opposite the direction of the original effect. Across settings, the Q statistic indicated significant heterogeneity in 11 (39%) of the replication effects, and most of those were among the findings with the largest overall effect sizes; only 1 effect that was near zero in the aggregate showed significant heterogeneity according to this measure. Only 1 effect had a tau value greater than .20, an indication of moderate heterogeneity. Eight others had tau values near or slightly above .10, an indication of slight heterogeneity. Moderation tests indicated that very little heterogeneity was attributable to the order in which the tasks were performed or whether the tasks were administered in lab versus online. Exploratory comparisons revealed little heterogeneity between Western, educated, industrialized, rich, and democratic (WEIRD) cultures and less WEIRD cultures (i.e., cultures with relatively high and low WEIRDness scores, respectively). Cumulatively, variability in the observed effect sizes was attributable more to the effect being studied than to the sample or setting in which it was studied.

We conducted preregistered replications of 28 classic and contemporary published findings with protocols that were peer reviewed in advance to examine variation in effect magnitudes across sample and setting. Each protocol was administered to approximately half of 125 samples and 15,305 total participants from 36 countries and territories. Using conventional statistical significance (p &lt; .05), fifteen (54%) of the replications provided evidence in the same direction and statistically significant as the original finding. With a strict significance criterion (p &lt; .0001), fourteen (50%) provide such evidence reflecting the extremely high powered design. Seven (25%) of the replications had effect sizes larger than the original finding and 21 (75%) had effect sizes smaller than the original finding. The median comparable Cohen’s d effect sizes for original findings was 0.60 and for replications was 0.15. Sixteen replications (57%) had small effect sizes (&lt; .20) and 9 (32%) were in the opposite direction from the original finding. Across settings, 11 (39%) showed significant heterogeneity using the Q statistic and most of those were among the findings eliciting the largest overall effect sizes; only one effect that was near zero in the aggregate showed significant heterogeneity. Only one effect showed a Tau &gt; 0.20 indicating moderate heterogeneity. Nine others had a Tau near or slightly above 0.10 indicating slight heterogeneity. In moderation tests, very little heterogeneity was attributable to task order, administration in lab versus online, and exploratory WEIRD versus less WEIRD culture comparisons. Cumulatively, variability in observed effect sizes was more attributable to the effect being studied than the sample or setting in which it was studied.

To examine the potential link between violent video game play and aggressive behavior, reliable and valid measures of the level of violence in video games are required. A range of different approaches have been used in the literature, and it is not clear to what extent they converge or measure different constructs. To address this question, three large longitudinal data sets covering at least 12 months were used from the United States (N ϭ 1,232), Singapore (N ϭ 3,024), and Germany (N ϭ 1,715). Violent content was measured through user ratings, expert ratings, and official agency ratings of individual titles as well as through expert ratings of game genres. The different measures were linked to aggressive behavior both cross-sectionally and longitudinally in all three countries and to the normative acceptance of aggression in Germany and Singapore. User ratings, expert ratings, and official agency ratings were found to be reliable. They showed substantial correlations within each culture as well as between the different cultures, indicating high convergent validity. Measures using nominations of game titles and measures using genre lists showed similar relationships with aggressive behavior and aggressive norms, both concurrently and prospectively over 12 months. Recommendations for a best practice approach to the assessment of violent content in video games are derived from the findings.

To address the longitudinal associations between adolescents' use of media violence and aggression, 1,715 high school students in Germany participated in 3 measurements over a 2-year period. Self-reported physical aggression and teacher-rated overall aggression were the outcome variables. A destructive testing approach showed that media violence predicted both self-reported physical aggression and teacher-rated aggression over 24 months, controlling for initial aggression as well as several sociodemographic and psychological covariates. Nonviolent media use was unrelated to self-reported or teacher-rated aggression. Latent growth mixture modeling identified 3 trajectories of use-stable low, stable high, and desistance-and parallel trajectories of self-reported physical aggression were found. Participants in the stable high group scored higher on aggressive behavior at the first wave than did stable low users. Desisters differed significantly from stable high users by showing a decrease in aggressive behavior over time. The findings are discussed in terms of the unique role of media violence use as a risk factor for adolescent aggression.

Several longitudinal studies and meta-analytic reviews have demonstrated that exposure to violent media is linked to aggression over time. However, evidence on effective interventions to reduce the use of violent media and promote critical viewing skills is limited. The current study examined the efficacy of an intervention designed to reduce the use of media violence and aggression in adolescence, covering a total period of about 12 months. A sample of 683 7th and 8th graders in Germany (50.1% girls) were assigned to two conditions: a 5-week intervention and a no-intervention control group. Measures of exposure to media violence and aggressive behavior were obtained about 3 months prior to the intervention (T1) and about 7 months post-intervention (T2). The intervention group showed a significantly larger decrease in the use of violent media from T1 to T2 than the control group. Participants in the intervention group also scored significantly lower on self-reported aggressive behavior (physical aggression and relational aggression) at T2 than those in the control group, but the effect was limited to those with high levels of initial aggression. This effect was mediated by an intervention-induced decrease in the normative acceptance of aggression. No gender differences in program efficacy were found. The results show that a 5-week school-based intervention can produce changes in the use of media violence, aggressive norms, and behaviors sustained over several months.

Peer groups are critical socialization agents for the development of social behavior in adolescence, but studies examining peer-group effects on individuals' prosocial behavior are scarce. Using a two-wave, multilevel data set (N = 16,893, 8481 male; 8412 female; mean age at Time 1: 14.0 years) from 1308 classes in 252 secondary schools in Germany, main effects of the classroom level of prosocial behavior, cross-level interactions between the classroom and the individual levels of prosocial behavior at Time 1, and the moderating role of gender were examined. The results showed that adolescents in classrooms with high collective levels of prosocial behavior at Time 1 reported more prosocial behavior at Time 2, about two years later, reflecting a class-level main effect. A significant cross-level interaction indicated that a high classroom level of prosocial behavior particularly affected individuals with lower levels of prosocial behavior at Time 1. The influence of samegender peers was larger compared with opposite-gender peers. The findings are discussed with respect to social learning mechanisms in the development of prosocial behavior and their implications for interventions to promote prosocial behavior.

In a longitudinal study with N = 1,854 adolescents from Germany, we investigated patterns of change and gender differences in physical and relational aggression in relation to normative beliefs about these two forms of aggression. Participants, whose mean age was 13 years at T1, completed self-report measures of physically and relationally aggressive behavior and indicated their normative approval of both forms of aggression at four data waves separated by 12-month intervals. Boys scored higher than did girls on both forms of aggression, but the gender difference was more pronounced for physical aggression. Physical aggression decreased and relational aggression increased over the four data waves in both gender groups. The normative acceptance of both forms of aggression decreased over time, with a greater decrease for the approval of physical aggression. In both gender groups, normative approval of relational aggression prospectively predicted relational aggression across all data waves, and the normative approval of physical aggression predicted physically aggressive behavior at the second and third data waves. A reciprocal reinforcement of aggressive norms and behavior was found for both forms of aggression. The findings are discussed as supporting a social information processing perspective on developmental patterns of change in physical and relational aggression in adolescence.

No abstract