Mediation analysis is built to answer not only if one variable affects another, but how the effect takes place. However, it lacks interpretable effect size estimates in situations where the mediator (an intermediate variable) and/or the outcome is categorical or otherwise non-normally distributed. By integrating a powerful approach known as average marginal effects within mediation analysis—termed Marginal Mediation Analysis (MMA)—the issues regarding categorical mediators and/or outcomes are, in large part, resolved. This new approach allows the estimation of the indirect effects (those effects of the predictor that affect the outcome through the mediator) that are interpreted in the same way as mediation analysis with continuous, normally-distributed mediators and outcomes. This also, in turn, resolves the troubling situation wherein the indirect plus the direct effect does not equal the total effect (i.e., the total effect does not equal the total effect). By offering this information in mediation, interventionists and lawmakers can better understand where efforts and resources can make the greatest impact. This project presents the development and the software of MMA, describes the evaluation of its performance, and reports an application of MMA to health data. The approach is successful in several aspects: 1) the software works across a wide variety of situations as the MarginalMediation R package; 2) MMA performed well and was statistically powered much like other mediation analysis approaches; and 3) the application demonstrated the increased amount of interpretable information that is provided in contrast to other approaches.

School safety is one of the most important issues facing administrators, teachers, and parents. Several risk factors have been identified as antecedents to aggression including poor social skills, difficulty dealing with anger and frustration, and inadequate problem solving abilities. No Child Left Behind requires all schools receiving Title IV funds to implement research based violence interventions. Second Step, an internationally recognized violence prevention curriculum published by Committee for Children was implemented in an urban elementary school with 66 African American students in grades 3 through 5 for 9 weeks. This study employed a randomized control group design with two treatment conditions; Second Step instruction and Second Step instruction with digital role-playing, an adaptation of digital storytelling, to increase program effectiveness and intensify student motivation. The School Social Behavior Scales-2 (Merrell, 2002) was used to assess differences in aggression and prosocial skills. MANOVA indicated significant differences for grade only. Older students had higher prosocial behavior scores and younger students had lower scores on the program's content assessment. Results indicated that the Second Step curriculum did not affect behavior. Although the benefits of teaching students to respond empathetically to others, solve problems, and control anger have been documented in the literature, the use of Second Step to accomplish these goals has not been supported. / Educational Psychology