Current Directions in Mediation Analysis

Abstract

Mediating variables continue to play an important role in psychological theory and research. A mediating variable transmits the effect of an antecedent variable on to a dependent variable, thereby providing more detailed understanding of relations among variables. Methods to assess mediation have been an active area of research for the last two decades. This paper describes the current state of methods to investigate mediating variables. Keywords mediation; indirect effect; statistical methodsMediating variables have been ubiquitous throughout the history of psychology because they are used to explain how or why two variables are related. One of the oldest models in psychology, the Stimulus → Organism → Response model, specifies mediating processes in an organism that transmit a stimulus to a response. A modern application of mediating variables is in treatment and prevention research, where interventions are designed to change mediating variables, such as norms, which are hypothesized to be causally related to a dependent variable, such as health behavior. The promise of mediation analysis is that it can identify fundamental processes underlying human behavior that are relevant across behaviors and contexts. Once a true mediating process is identified, then more efficient and powerful interventions can be developed because these interventions can focus on variables in the mediating process. A variety of mediation-analysis methods, including statistical and experimental methods, have been used throughout the history of psychology. New developments in mediation analysis extract more accurate information about whether a variable truly mediates the relation between two other variables.Consider some examples of mediating variables in psychology: (a) A tobacco prevention program, the antecedent variable, reduces cigarette smoking by changing the social norms for tobacco use, the mediating variable; (b) exposure to negative life events affects blood pressure through the mediation of cognitive attributions to stress; or (c) instructing persons to make images of words in a memory task increases the number of images made, the mediating variable, which improves recall of the words. In each case, an antecedent variable affects a mediator variable and the mediator variable affects a dependent variable, thus forming a chain of relations among the three variables (Baron & Kenny, 1986;. The chain of relations among the variables is called an indirect or mediated effect of the antecedent variable on the dependent variable. An effect that is not mediated this way is called a direct effect. Although the consideration of a mediating variable may

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