Robustness of Statistical Power in Group-Randomized Studies of Mediation Under an Optimal Sampling Framework

Abstract

Abstract. When planning group-randomized studies probing mediation, effective and efficient sample allocation is governed by several parameters including treatment-mediator and mediator-outcome path coefficients and the mediator and outcome intraclass correlation coefficients. In the design stage, these parameters are typically approximated using information from prior research and these approximations are likely to deviate from the true values eventually realized in the study. This study investigates the robustness of statistical power under an optimal sampling framework to misspecified parameter values in group-randomized designs with group- or individual-level mediators. The results suggest that estimates of statistical power are robust to misspecified parameter values across a variety of conditions and tests. Relative power remained above 90% in most conditions when the incorrect parameter value ranged between 50% and 150% of the true parameter.