Methodological Challenges Examining Subgroup Differences: Examples from Universal School-Based Youth Violence Prevention Trials

This article reviews the literature on school-based universal prevention programs to illustrate key methodological challenges for investigating subgroup differences in prevention effects. The variety of potential moderating factors examined within this literature is discussed within the context of a social-ecological model. This literature is used to illustrate methodological challenges to examining subgroup differences in intervention effects. These findings include the need for a clear a priori theoretical basis for selecting factors to examine, concerns over Type I error rates that result from large numbers of comparisons, the failure to provide explicit tests of moderation, interpretive issues arising from a restricted range on moderator variables, the failure to report effect size estimates, the need to examine potential confounding factors, and the challenge of examining factors that might operate at multiple levels. These points are illustrated by examples of studies, primarily within youth violence prevention research, that have identified factors within the individual, school, and community that moderate the outcomes of preventive interventions. We conclude with general recommendations for future work. These include the benefits of using the social-ecological model to provide a basis for moving from exploratory to more theory-driven confirmatory models of subgroup differences, the potential merits of qualitative research designed to identify factors that may influence the effectiveness of intervention efforts for specific subgroups of individuals, and the provision of effect size estimates and confidence intervals for effect sizes in prevention reports.