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st: Categorical mediators and ordinal outcome: using Jackknife to compute the variance of the difference between coefficients


From   Fernanda Queiros <nandaqueiros@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Categorical mediators and ordinal outcome: using Jackknife to compute the variance of the difference between coefficients
Date   Mon, 2 Apr 2012 16:33:02 -0400

Dear list participants,

First of all, I am a PhD student with limited statistical knowledge
compared to what I’ve seen here at the list. Also, English is not my
first language; so, forgive me if any part of the message is not
crystal clear.

I am trying to estimate the mediation effect for an ordinal outcome
with 10 levels (ladderw4). The two mediators I’m interested are
categorical. My main independent variable (IV) is categorical (four
levels), as well as all my co-variates. I am using complex survey
data, with 132 PSU’s and 4 strata. I saw here at the list some
suggestions applying econometrics methods to a question about testing
mediation with categorical mediators, which is beyond my knowledge.

Thus, I am trying to compute the difference of my main IV’s
coefficients (from the models with and without the mediator) to
measure the change and, therefore, mediation effect. I am thinking
about using the jackknife procedure to estimate the variance of my
coefficients. However, the problem I am facing is that I don’t know
how to compute the variance of the difference…

That is how I am establishing the survey design using Jackknife (Stata 11.2):

. svyset psuscid [pweight=gswgt4_2], strata(region) vce(jackknife)

I am, then, using svy: ologit to run my models: (1) without the
mediator and (2) with it:

(1) xi: svy,subpop(subpop2): ologit ladderw4 i.type_disability age_w4
bio_sex_ i.racew1_r i.parented i.famst3

(2) xi: svy,subpop(subpop2): ologit ladderw4 i.type_disability age_w4
bio_sex_ i.racew1_r i.parented i.famst3 deprew1_dic

The output gives me the “final” coefficients and Jackknife SE’s for my
IV’s. My question is:

- Is there a way to get the coefficients/SE’s for each one of the 132
replications Stata is running in this case? I think that with this
information it would be possible to compute the variance of the
difference between the two coefficients of my main IV...

 - Also, does any one have experience on testing mediation with
similar types of variables (using complex survey data) and would
suggest me a different approach from what I am trying to do?

Looking forward to hearing your ideas/suggestions!

Many thanks,

Fernanda



--
Fernanda Queirós
Me., Fonoaudióloga / M.S., Brazilian Speech-Language Pathologist
Doutoranda - Bolsista CAPES/Fulbright / Ph.D. Candidate -
CAPES/Fulbright grantee
University of North Carolina at Chapel Hill
Gillings School of Global Public Health
Department of Maternal and Child Health


Para ser grande, sê inteiro: nada teu exagera ou exclui. Sê todo em
cada coisa. Põe quanto és
no mínimo que fazes....
(Fernando Pessoa)

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