Differential effects refer to the phenomenon where the same treatment or intervention can have varying impacts on different groups of individuals or in different contexts. This research area seeks to understand why and how these differences occur, and how they can be addressed to improve the effectiveness of interventions. Factors that may contribute to differential effects include characteristics of individuals (e.g. age, gender, ethnicity), environmental factors, and the way the intervention is implemented. Understanding these differential effects can help researchers and practitioners tailor interventions to better meet the needs of diverse populations.