Mediator and moderator variables in nursing research: Conceptual and statistical differences

Mediators and moderators are variables that affect the association between an independent variable and an outcome variable. Mediators provide addition al information about how or why two variables are strongly associated. In c ontrast, moderators explain the circumstances that cause a weak or ambiguou s association between two variables that were expected to have a sirens rel ationship. Mediators and moderators are often overlooked in research design s, or the terms are used incorrectly. This article summarizes the conceptua l differences between mediators and moderators. The statistical analysis of moderators and mediators in multiple regression is briefly described and t wo examples are presented. (C) 2000 John Wiley & Sons, Inc.