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Re: st: Binary panel data questions

From   Maarten Buis <>
Subject   Re: st: Binary panel data questions
Date   Wed, 8 Feb 2012 10:27:15 +0100

On Wed, Feb 8, 2012 at 1:19 AM, Kim Peeters wrote:
> 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.

In essence you do not have panel data, you could just as well use the
first observation in each person and do a regular -logit-. I just
don't think there is any more information present in your data, and no
amount of fancy modeling can invent information that isn't present in
the data.

I would really check again whether that constant disease status isn't
some error during data preparation or some artifact of the way the
data was collected, as that a) sounds really suspicious and b) is
causing you this problem.

Hope this helps,

Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen

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