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st: Perfect predictors of an occurrence (survival analysis)

From   "Luis Ortiz" <>
To   "''" <>
Subject   st: Perfect predictors of an occurrence (survival analysis)
Date   Thu, 13 Mar 2008 13:21:05 +0100

Dear Statalisters,

I'm analysing the occurrence of the following event: getting out of
employment if you are over-educated. I'm doing so for a number of
over-educated individuals, using panel data. The spells are the periods in

I am especially interested by the type of contract. This is one of my main
independent variables. Therefore, I have split the initial variable in the
corresponding dummies, in order to include them in the analysis. Yet, I have
found that each one of these dummies perfectly predict the occurrence of the
event I'm studying. It might be because the spells are not very long and the
job, no matter how over-qualified it is, goes associated with a given type
of contract. In other words, the type of contract does not change during the

In such a case, dummy covariates on type of contract are not feasible for
the analysis. They perfectly predict the occurrence of the event.

Yet, this does not mean that over-educated workers are equally likely to get
out of employment REGARDLESS of their type of contract. Moreover, I suspect
that the type of contract may be associated to a different likelihood of
getting out of the employment.

How could I overcome the problem I have mentioned for running survival
analysis? Is there any alternative way to estimate the relative likelihood
of temporary / permanent over-educated workers quitting their jobs that you
come up with?

I do appreciate your attention

Best regards

Luis Ortiz

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