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Re: Re: st: RE: SEM with bootstrapping for analysis of mediation


From   "Iyer, Neeraj N" <niyer@purdue.edu>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: Re: st: RE: SEM with bootstrapping for analysis of mediation
Date   Wed, 11 Jul 2012 20:13:56 -0400

Dear Phil,

Thank you. I did not want to assume that the direct and indirect effects would be adjusted for the covariates; your note is helpful in that regard.  

However, in the command line  sem (MV <- IV CV1 CV2 CV3 CV4 ) (DV <- MV IV CV1 CV2 CV3 CV4), I was unable to fathom how STATA would know which one of IV/CV1/CV2/CV3/CV4 is the true Indep. Var.  In other words, since " IV CV1 CV2 CV3 CV4" are common to both paths how can STATA differentiate between the variables, which will answer the question, "Whose indirect effect are we observing"? 

Hence, I was looking for bootstrap CI for the indirect effect of each individual variable, or a partitioned bootstrap CI.  Is this partitioning plausible?

Thanks and regards,
Neeraj

On Wed, Jul 11, 2012 at 7:49 PM, Philip Ender <ender97@gmail.com> wrote:
...

However when I ran a mediation model with one IV and 4 other
covariates i.e. sem (MV <- IV CV1 CV2 CV3 CV4 )(DV <- MV IV CV1 CV2
CV3 CV4), the bootstrap confidence intervals I obtained were for the
overall direct, indirect and total effects and not broken down by each
variable.  I wish to obtain the bootstrap CI separately for my IV
adjusted for other covariates.  Any thoughts about approaching this
problem?

Another question is why is the seed set at 358395?  What is this
number's significance?
...

Dear Neeraj,

Since the covariates CV1-CV4 are included in each of the two equations
of the -sem- command in the -indirect.ado program the direct and
indirect effects are adjusted for these four covariates.  I'm not sure
what you are asking for when you say you wish  to obtain the bootstrap
CI
separately for my IV adjusted for other covariates.

The -set seed- is included so that readers can reproduce the results
from the example.  The number has no special meaning.

--
Phil Ender
UCLA Statistical Consulting Group
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-- 
Neeraj
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