APA Dictionary of Psychology

in the study of causal effects, the total extent to which the dependent (or outcome) variable is changed by the independent (or predictor) variable, including any indirect effect through a mediator. In a simple example, if the independent variable, x, is presumed to cause the outcome variable, y, the path coefficient of this direct effect, A, is the total effect. If there is an intervening variable, linked by two path coefficients, B and C, this indirect effect is BC, and the total effect is A + BC. See also path analysis.