[Mediation-information] Causally dependent mediators

[Teppei Yamamoto]

Hi Angel,

The second model does not give you estimates of those effects "net of 
deprivation" -- you will get the direct and indirect effects of 
manipulating education levels from one level to another on aging.

Including deprivation as a covariate in the models allows you to correct 
the confounding between education and economic position and/or education 
and aging due to deprivation, but that does not allow you to interpret 
the estimated mediation/direct effects as those effects "net of" 
deprivation.

If you are interested in how the effect of deprivation on aging is 
transmitted by those two interrelated mediators, you want to use 
multimed (as in your original message) instead of model 2.

Best,
Teppei

(8/27/14, 10:35 AM), Angel Rodriguez wrote:
>
> Thank you for your answers, Teppei.
>
> So, would these two models make sense?
>
> 1) deprivation --> education level --> aging well (covariates: age,
> gender, region)
> (with R mediation package, to study the direct and indirect effects of
> deprivation on aging well)
>
> 2) education level --> economic position --> aging well (covariates:
> DEPRIVATION, age, gender, region)
> (with R mediation package, to study the direct and indirect effecs on
> education on aging well, net of deprivation)
>
> Best,
>
> Angel
>
> -----Mensaje original-----
> De: mediation-information-bounces at lists.r-forge.r-project.org en nombre
> de Teppei Yamamoto
> Enviado el: mié 27/08/2014 15:27
> Para: Mediation-information at r-forge.wu-wien.ac.at
> Asunto: Re: [Mediation-information] Mediation-information Digest, Vol
> 25, Issue 3
>
> Hi Angel,
>
> The difference between the two estimates (multimed vs. mediation
> analysis on education level as the "treatment") is that the former is
> about the effect of manipulating infant deprivation on aging whereas the
> latter is about the effect of manipulating education directly. That is,
> they are estimating effects of different kinds of hypothetical
> interventions and how they are transmitted through the variables that
> are assumed to be causally descendant.
>
> So I think your choice boils down to what causal quantity you are trying
> to estimate.
>
> Best,
> Teppei
>
>
> (8/27/14, 5:38 AM), Angel Rodriguez wrote:
>  > Thank you again, Mashhood.
>  >
>  > What I do not understand yet is why we need a package like multimed if
>  > we can decompose a model with two causally dependent mediators (infant
>  > deprivation --> education level --> economic position --> aging well)
>  > into two models (infant deprivation --> education level --> aging well &
>  > education level --> economic position --> aging well).
>  >
>  > Following your advise, I should include infant deprivation as a
>  > confounder in the model education level --> economic position --> aging
>  > well. But if deprivation conditions education strongly, I could end not
>  > finding any direct nor indirect effect of education on aging well.
>  >
>  > Best regards,
>  >
>  > Angel Rodriguez-Laso
>  >
>  >
>  > -----Mensaje original-----
>  > De: mediation-information-bounces at lists.r-forge.r-project.org en nombre
>  > de Mashhood Sheikh
>  > Enviado el: mar 26/08/2014 20:56
>  > Para: mediation-information at lists.r-forge.r-project.org
>  > Asunto: Re: [Mediation-information] Mediation-information Digest, Vol
>  > 25,Issue 3
>  >
>  >
>  > Hi,
>  >
>  > In the model (education level --> economic position --> aging well) you
>  > should include all the variables that potentially confound the
>  > association between education level and economic position, education
>  > level and ageing well, and economic position and ageing well.
>  >
>  > Best wishes,
>  > Mashhood
>  > ---
>  > Mashhood Ahmed Sheikh
>  > Research Fellow,
>  > Department of Community Medicine
>  > Faculty of Health,
>  > University of Tromsø,
>  > Norway
>  >
>  >
>  >
>  >
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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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-- 
====================================
Teppei Yamamoto
Assistant Professor
Department of Political Science
Massachusetts Institute of Technology
http://web.mit.edu/teppei/www/
====================================