[Mediation-information] Interaction between exposures?

[Kosuke Imai]

You can think of it as the four-category exposure.  Now, the definition of indirect effects is a little bit different: in Y(t,M(t)) - Y(t,M(t’)) you have to pick t and t’.  In the binary treatment case, this choice is obvious because there are only two values; t=1, t’= 0.  When you have four category exposure, depending on your substantive question, you can pick different comparisons. 

Best,
Kosuke

Department of Politics
Princeton University
http://imai.princeton.edu

On Nov 28, 2013, at 7:19 AM, Mashhood Sheikh <senor_massao at hotmail.com> wrote:

> Dear Dustin and Kosuke,
>  
> Is it possible to estimate the direct and indirect effects when there is an interaction between exposures (X1, X2), regressed on outcome Y? Since X2 is also a mediator-outcome confounder between the mediation model X1>M>Y, and X1 is also a mediator-outcome confounder between the mediation model X2>M>Y, it is important to include them in the model as covariates, but than what about the interaction between them? Note: all variables, X1, X2, M, and Y are binary.
> 
> I would highly appreciate any tips...
> 
> 
> Thankfully,
> Mashhood
> Institute of Community Medicine,
> University of Tromsø,
> Norway.
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