Interactions do not only tell us when, but can also tell us how: Testing process hypotheses by interaction

Hypotheses about psychological processes are often tested using traditional mediation analysis. This analysis relies on measurement of a transmitting variable. Conducting this analysis has become almost synonymous with examining process hypotheses. An alternative strategy to mediation analysis (the Testing-a-Process-hypothesis-by-an-Interaction Strategy, TPIS) is illustrated here. TPIS is based on a fully experimental design whereby a hypothesized process is tested by an interaction between the hypothesized cause of an effect and a contextual variable. In the interaction term, the contextual variable allows comparison of the causal effect observed when the process is uninterrupted to the effect observed when the process is interrupted. Thus, TPIS translates a theoretical process hypothesis into a statistical interaction hypothesis that uses a fully experimental design to directly examine the hypothesized process. Copyright © 2010 John Wiley & Sons, Ltd.