Author guidelines for journals could help to promote transparency, openness, and reproducibility

This article reviews the observational, laboratory, and field experimental literatures on interventions for reducing prejudice. Our review places special emphasis on assessing the methodological rigor of existing research, calling attention to problems of design and measurement that threaten both internal and external validity. Of the hundreds of studies we examine, a small fraction speak convincingly to the questions of whether, why, and under what conditions a given type of intervention works. We conclude that the causal effects of many widespread prejudice-reduction interventions, such as workplace diversity training and media campaigns, remain unknown. Although some intergroup contact and cooperation interventions appear promising, a much more rigorous and broad-ranging empirical assessment of prejudice-reduction strategies is needed to determine what works.

Can the media reduce intergroup prejudice and conflict? Despite the high stakes of this question, understanding of the mass media's role in shaping prejudiced beliefs, norms, and behavior is limited. A yearlong field experiment in Rwanda tested the impact of a radio soap opera featuring messages about reducing intergroup prejudice, violence, and trauma in 2 fictional Rwandan communities. Compared with a control group who listened to a health radio soap opera, listeners' perceptions of social norms and their behaviors changed with respect to intermarriage, open dissent, trust, empathy, cooperation, and trauma healing. However, the radio program did little to change listeners' personal beliefs. Group discussion and emotion were implicated in the process of media influence. Taken together, the results point to an integrated model of behavioral prejudice and conflict reduction that prioritizes the communication of social norms over changes in personal beliefs.

How can we change social norms, the standards describing typical or desirable behavior? Because individuals' perceptions of norms guide their personal behavior, influencing these perceptions is one way to create social change. And yet individuals do not form perceptions of typical or desirable behavior in an unbiased manner. Individuals attend to select sources of normative information, and their resulting perceptions rarely match actual rates of behavior in their environment. Thus, changing social norms requires an understanding of how individuals perceive norms in the first place. We describe three sources of information that people use to understand norms-individual behavior, summary information about a group, and institutional signals. Social change interventions have used each source to influence perceived norms and behaviors, including recycling, intimate-partner violence, and peer harassment. We discuss conditions under which influence over perceived norms is likely to be stronger, based on the source of the normative information and individuals' relationship to the source. Finally, we point to future research and suggest when it is most appropriate to use a norm change strategy in the interest of behavior and social change.Researchers, policymakers, and practitioners do their best to measure actual rates of behaviors in a community, such as the number of people who engage in recycling, domestic violence, voting, or peer harassment. These rates are often discussed as the community's "norm"-e.g., "it is the norm to recycle here; most citizens recycle," or, "domestic violence is not normative in this community; only 2% of residents report that domestic violence is acceptable."Psychologists focus on measuring a different kind of norm-not the actual norm, but community members' subjective perceptions of the norm. There are two reasons for this focus on subjective perceptions. First, unlike statisticians and policymakers, the average person does not know the actual rates of behaviors or opinions in their community, such as recycling or approval of domestic violence.

.The authors wish to note the following: "We reported an estimated 30% decrease in administrative reports of conflict and would like to correct this estimate to 25%. The original paper reported this estimate as the rounded covariate-adjusted estimated average treatment effect (−0.06) divided by the rounded unadjusted control group mean (0.20). Without the rounding error, the original estimate is 29%. Using both covariate adjusted estimates, we have an estimate of 25%. Using both unadjusted estimates, we have an estimate of 23%. The original estimate of 30% was reported in the Abstract (line 11), the Significance Statement (line 8), in the results on page 569 (left column, first paragraph, line 9), and in the discussion on page 571 (left column, first paragraph, line 6). In each of these places, we would like to replace the number 30 with 25. The estimated overall effects on administrative reports of conflict remain statistically insignificant at the α=0.05 level."Published under the PNAS license.