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Abstract

In a simple mediation model, the effect of a manipulated variable X on a dependent variable Y over and above the effect of the mediator Me can be estimated by regressing Y on X and Me. The impact of X on Y in such a model is adjusted for the relationship both between X and Me and between Me and Y. The authors examine the adjustment function in the context of a 2 × 2 design with two manipulated variables. In such a situation, the mediator could be affected by either one of the main effects and/or the interaction between two manipulated variables. To adjust for the impact of the mediator, a standard procedure has been to rely on an ANCOVA that includes only the mediator. The authors show, both analytically and with simulations, that this leads to improper control of the mediator and to biased estimates of the model parameters.

Keywords

mediation ANCOVA adjustment regression

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References

Baron, R.M. , & Kenny, D.A. (1986). The moderator-mediator variable distinction in social psychological research: Conceptual, strategic, and statistical considerations . Journal of Personality and Social Psychology, 51, 1173-1182.

Grandey, A.A. , Fisk, G.M. , Mattila, A.S. , Jansen, K.J. , & Sideman, L.A. (2005). Is ``service with a smile'' enough? Authenticity of positive displays during service encounters. Organizational Behavior and Human Decision Processes, 96, 38-55.

Judd, C.M. , & McClelland, G.H. (1989). Data analysis: A model comparison approach. San Diego, CA: Harcourt, Brace, Jovanovich.

MacKinnon, D.P. , Lockwood, C.M. , Hoffman, J.M. , West, S.G. , & Sheets, V. (2002). A comparison of methods to test mediation and other intervening variable effects. Psychological Methods , 7, 83-104.

MacKinnon, D.P. , Warsi, G. , & Dwyer, J.H. (1995). A simulation study of mediated effect measures . Multivariate Behavioral Research, 30, 41-62.

Muller, D. , Judd, C.M. , & Yzerbyt, V. (2005). When moderation is mediated and mediation is moderated . Journal of Personality and Social Psychology, 89, 852-863.

Yzerbyt, V. , Muller, D. , & Judd, C.M. (2004). Adjusting researchers' approach to adjustment: On the use of covariates when testing interactions. Journal of Experimental Social Psychology, 40, 424-431.

Adjusting for a Mediator in Models With Two Crossed Treatment Variables

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