Abstract: This article described three common multilevel mediation models. According to hierarchical linear model and causal steps approach, inspection procedures of multilevel mediation effect and method of estimating mediation effect size were elaborated. Group mean centering with the means reintroduced into the level-2 intercept model would provide an appropriate test of 2-1-1 and 1-1-1 mediation model, because this centering method could decompose multilevel mediation effects into within-group and between-group effects. This article also discussed the future direction of multilevel mediation model, which is multilevel moderated mediation and Multilevel Structural Equations Modeling, and the extension of testing methods, namely, Sobel test and confidence interval testing method.

Key words: multilevel, mediation, hierarchical linear model, centering