I would like to test for mediated moderation as in the attached path diagram.
I obsered that the effect of binary treatment (X) on behavioral outcome (Y) depends largely on the moderator (Mod). I want to test whether the moderation is (partly) explained by subjects perceptions of the intervention (Med).
Any idea how to perform this in SPSS, R, or Stata?
Any publications concerning these methods are highly appreciated.
I found the answer myself in Morgan-Lopez & MacKinnon, 2006. Demonstration and evaluation of a method for assessing mediated moderation. Behavior Research Methods 38(1), 77-87. The model corresponds to model 8 in SPSS PROCESS. Instead of defining the model the way I did in my question, one needs to create the interaction variable seperately, as shown in the paper.
Also, chapter 12 in Hayes, A., 2018. Introduction to mediation, moderation, and conditional process analysis: A regression-based approach. gives an overview and critical discussion of these types of models.
I would also have proposed the Hayes sources. But you should keep in mind that it is not only the statistical structure that is necessary to establish mediation, but also the temporal structure of the assessement of the indvidual variables. To be sure that it is a causal chain you would need a longitudinal analysis. Cross-sectional studies cant really show causality.
Dear Rainer,
I know, that is exactly my problem. However, my current argument is that I do not claim causality. I only say that the mediator partly predicts the behavioral outcome and that further studies are needed to establish causality by also manipulating the mediator. I am not sure whether the study then is still interesting, especially since I do not find evidence for a (substantial) mediation of the moderation. However, I do not want to leave the analysis out only because I do not find evidence, since from my point of view it makes sense theoretically/conceptually to make this analysis. Just don't have enough experience with publication in psych/social psych to know how this might turn out.
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