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st: Modeling Paired Longitudinal - Covariance question

From   Jennifer A Hoff <>
Subject   st: Modeling Paired Longitudinal - Covariance question
Date   Tue, 21 Dec 2010 09:05:25 -0500

The dataset I am working with is panel data �ongitudinal with 
measurements in 2007,2008 and 2009.
I ran the model

 xtset idnum year
xtgee outcome  $demog  $comobid_$covariates  Med_group $yearlist 
$MedgroupYear, family(gamma)link(power -0.5) robust i(idnum )
Next ran the data through a propensity score matching  (one to one match) 
on Med_Group.  A variable called pair  identifies which observations were 
matched.  Each member of the duo is assigned the same value for the 
variable pair.
I want to re-run the above model on the propensity matched subset of the 
original data .  I realize the covariance structure needs adjusting for 
the matched propensity pair.  I have correlations between the repeated 
measures of an individual - (accounted for with the xtset statement). But 
I also have a correlation between the patient in Med_Group A that was 
propensity matched/paired to a patient in Med_Group B.   How do I adjust 
the model to accommodate that?

Jennifer Hoff Lindquist
Health Services Research and Development
Mailing Address: 
VA Medical Center
508 Fulton Street (152)
Durham, NC 27705
(919) 286-0411 Ext. 4054 (New as of 5/18/09)

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