[Mediation-information] moderated mediation analysis using 'mediation' package

[Teppei Yamamoto]

Hi Liviu,

Moderated mediation is supported in the mediation package as of the most 
recent update (4.0), which we were about to announce to the list 
subscribers. Your code looks correct except the last step, where you 
need to use the "covariates" argument and specify the value of the 
moderator on which the estimate will be conditioned. (Also, you may want 
to consider including a three-way interaction in the outcome model, but 
that's your call.) Go ahead and download the current version of the 
package, and see the help document and example to find out the specifics.

Best,
Teppei


(3/22/12 12:16 PM), Liviu Andronic wrote:
> Dear package developers
> I have a question regarding the 'mediation' package. Am I correct in
> understanding that mediate() allows to estimate 'moderated mediated
> regression' models? I am thinking specifically of Edwards and Lambert
> (2007) and their (cumbersome?) SPSS macro&  Excel spreadsheet approach
> [1][2]. I am writing to you since I found no mention of 'moderat' in
> your package vignette, but given the flexibility of the package it
> seems to me that it supports the use case in [2].
>
> Consider the following example:
> #Assume: M=TRUST (mediator), X=EVPUBLIC, Z=ENGAGESP (mediator)
>
> #Then estimate eq5 of the paper
> mod.m2<- lm(TRUST ~ ENGAGESP * EVPUBLIC, modmed)
>
> #Estimate eq20 of the paper
> mod.y2<- lm(COMMITMENT ~ TRUST * ENGAGESP + EVPUBLIC +
> ENGAGESP:EVPUBLIC, modmed)
>
> #Estimate the mediation effects
> med_b<- mediate(mod.m2, mod.y2, dropobs=F, treat='EVPUBLIC',
> mediator='TRUST', boot=T, sims=1000)
>
> To the best of my understanding, the last call should generate sound
> results. Am I correct in this?
>
> Regards
> Liviu
>
> [1] http://public.kenan-flagler.unc.edu/faculty/edwardsj/downloads.htm
> [2] http://public.kenan-flagler.unc.edu/faculty/edwardsj/modmed.zip
>
>
>

-- 
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Teppei Yamamoto
Assistant Professor
Department of Political Science
Massachusetts Institute of Technology
http://web.mit.edu/teppei/www/
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