instrumental variable

mediation analysis

indirect effects

detect moderating effects

multiple regression

effect size

instrumental variables

age period cohort

causal effects

British journal of mathematical & statistical psychology/British journal of mathematical and statistical psychology

Virtually all discussions and applications of statistical mediation analysis have been based on the condition that the independent variable is dichotomous or continuous, even though investigators frequently are interested in testing mediation hypotheses involving a multicategorical independent variable (such as two or more experimental conditions relative to a control group). We provide a tutorial illustrating an approach to estimation of and inference about direct, indirect, and total effects in statistical mediation analysis with a multicategorical independent variable. The approach is mathematically equivalent to analysis of (co)variance and reproduces the observed and adjusted group means while also generating effects having simple interpretations. Supplementary material available online includes extensions to this approach and Mplus, SPSS , and SAS code that implements it.

Statistical mediation analysis with a multicategorical independent variable