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st: Binary panel data questions


From   Kim Peeters <kimpeeters84@yahoo.com>
To   Statalist <statalist@hsphsun2.harvard.edu>
Subject   st: Binary panel data questions
Date   Tue, 7 Feb 2012 16:19:31 -0800 (PST)

Dear Statalist,

I am trying to analyze an unbalanced panel data set. It contains yearly data on a fairly large number of patients and spans almost twenty years. The dependent variable is binary and equal to zero if the patient does not have a certain ailment and equal to one if he/she does. The study endeavors to test for a relationship between the outcome (no illness vs. illness) and a group of independent variables. No drugs or treatments were administered.

Somewhat remarkably, it turns out that none of the participants in the study experienced a transition from one state to the other state (e.g. transition from no ailment to ailment and vice versa). In other words, all patients that did not suffer from the illness at the onset of the study remained disease-free and all patients that did suffer from the illness at the onset of the study continued to be ill.

Originally, I planned to use -xtlogit- with fixed effects to control for unobserved influences that differ between patients but remain constant in a given patient. However, since none of patients experienced a transition, Stata correctly returns error code 2000: outcome does not vary in any group.

At the moment, I do not know which statistical technique would be the most appropriate. Recall that I try to test for a relationship between the outcome (no illness vs. illness) and a group of independent variables.  I thought about running a logistic regression with clustered standard errors (i.e. vce(cluster ID)). However, I do not want to discard the time dimension in the panel data and I would to correct for potential omitted variable bias.

Any suggestion?

Thank you!

Kim Peeters


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