A partial posterior p value test for multilevel mediation

Abstract

A variety of inferential tests are available for single and multilevel mediation but most come with notable limitations that balance tradeoffs between power and Type I error. We extend the partial posterior p value method (p3 method) to test multilevel mediation. This contemporary resampling‐based composite approach is specifically suited for complex null hypotheses. We develop the p3 method and investigate its performance within the context of two‐level cluster‐randomized multilevel mediation studies. Similar to its performance in single‐level studies, we found that the p3 method performed well relative to other mediation tests suggesting it provides a judicious balance between Type I error rate and power. While bias‐corrected bootstrapping achieved the best overall performance, the p3 method serves as an alternative tool for researchers investigating multilevel mediation that is especially useful when conducting a priori power analyses. To encourage utilization, we provide R code for implementing the p3 method.