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st: "Separation" issue in clustered/Longitudinal binary data.

From   <>
Subject   st: "Separation" issue in clustered/Longitudinal binary data.
Date   Tue, 21 Dec 2010 20:10:56 -0600 (CST)

Hi, The STATA-community members,

Hope you have a great holiday.

I am now working on a longitudinal dataset. The outcome variable is a binary variable (a patient-reported drug's side effect) with repeated measures for three waves. Now I have an intervention (whether the participant received the drug), and I have used xtgee, xtlogit and xtmelogit to model the effects of this intervention on the outcome in a few different ways. However, no matter which method I used, I always encountered the separation issue. 

In fact, I have tried the "firthlogit" ado file to model the baseline data - and yes, it worked very well and has largely reduced the biases. However, I wonder, is there any ado file I can use to adjust for the bias in the longitudinal dataset? I have searched online for hours but can't find any. I also looked into R package, but I found nothing either. Any suggestion? 

Thanks so much!

Cheenghee M. Koh, MSW
PhD Student (4th year)
School of Social Service Administration
University of Chicago
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