Mediators and moderators in early intervention research.
OBJECTIVE
The goal of this paper is to provide clarification with regard to the nature of mediator and moderator variables and the statistical methods used to test for the existence of these variables. Particular attention will be devoted to discussing the ways in which the identification of mediator and moderator variables may help to advance the field of early intervention in psychiatry.


METHODS
We completed a literature review of the methodological strategies used to test for mediator and moderator variables.


RESULTS
Although several tests for mediator variables are currently available, recent evaluations suggest that tests which directly evaluate the indirect effect are superior. With regard to moderator variables, two approaches ('pick-a-point' and regions of significance) are available, and we provide guidelines with regard to how researchers can determine which approach may be most appropriate to use for their specific study. Finally, we discuss how to evaluate the clinical importance of mediator and moderator relationships as well as the methodology to calculate statistical power for tests of mediation and moderation.


CONCLUSIONS
Further exploration of mediator and moderator variables may provide valuable information with regard to interventions provided early in the course of a psychiatric illness.
Breitborde
Nicholas J K
NJ
Department of Psychiatry, University of Arizona, Tucson, Arizona 85724-5002, USA. breitbor@email.arizona.edu
Srihari
Vinod H
VH
Pollard
Jessica M
JM
Addington
Donald N
DN
Woods
Scott W
SW
D006801:Humans; D001523:Mental Disorders / Q000628:therapy*; D008605:Mental Health Services; D008960:Models, Psychological; D015233:Models, Statistical; D012106:Research; D012307:Risk Factors; D013997:Time Factors