How and why criteria defining moderators and mediators differ between the Baron & Kenny and MacArthur approaches.

OBJECTIVE In recognition of the increasingly important role of moderators and mediators in clinical research, clear definitions are sought of the two terms to avoid inconsistent, ambiguous, and possibly misleading results across clinical research studies. DESIGN The criteria used to define moderators and mediators proposed by the Baron & Kenny approach, which have been long used in social/behavioral research, are directly compared to the criteria proposed by the recent MacArthur approach, which modified the Baron & Kenny criteria. RESULTS After clarifying the differences in criteria between approaches, the rationale for the modifications is clarified and the implications for the design and interpretation of future studies considered. CONCLUSIONS Researchers may find modifications introduced in the MacArthur approach more appropriate to their research objectives, particularly if their research might have a direct influence on decision making.