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Re: st: medeff command negative percentage of total effect mediated


From   Maria Chatzivasileiadi <mariachatzivasileiadi@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: medeff command negative percentage of total effect mediated
Date   Tue, 4 Jun 2013 18:20:25 +0100

Dear Ariel,

Thank you very much for your reply. I hadn't read this article and it
does provide some useful references that I will go through.
I had a priori hypothesized that the indirect and direct effects would
be at opposite directions, what I am not sure is whether the program
takes into account that it is dividing a positive by a negative sign
and therefore gives a negative percentage of total effect mediated.
Have you used it before and encountered something similar?

Many thanks,
Maria

2013/6/4 Ariel Linden, DrPH <ariel.linden@gmail.com>:
> This not an unusual finding, and it is discussed in almost every paper on
> mediation. I suggest you read the paper by Adam Glynn* as a starting point.
> You can go from there to his reference list to learn more if that does not
> suffice
>
> *Glynn, A.N.: The product and difference fallacies for indirect effects. Am.
> J. Political Sci. 56, 257-269 (2012)
>
> Ariel
>
> Date: Mon, 3 Jun 2013 11:16:20 +0100
> From: "worldpatient ." <worldpatient@gmail.com>
> Subject: st: medeff command negative percentage of total effect mediated
>
> Dear Statalisters,
>
> I am using the user-written command -medeff command in Stata/IC 11 for
> Windows to test for causal mediation effects.
> My outcome is binary and my mediator is continuous.
>
> My question has to do with the interpretation of the percentage and
> 95%CIs of total effect mediated. In my analysis, the direct and total
> effects although not significant are negative while the indirect
> effect is positive and very small.
> As a result the percentage of the total effect mediated is negative
> and the CIs range from -203 to 46..
>
> Is there a way that I could interpret the percentage of the total
> effect mediated and the CIs when this percentage is negative and the
> CIs are so wide?
>
> Many thanks,
> Maria
>
>
>
>
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