segmented time dependent variable Cox regression

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leoniec
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Joined: Wed Aug 01, 2012 11:14 am

segmented time dependent variable Cox regression

Postby leoniec » Wed Aug 01, 2012 1:01 pm

Hi

I am trying to do a Cox regression with a time dependent variable. Time zero is time of diagnosis and follow up ends when patient has admission or is censored. I am interested in seeing whether a particular intervention reduces risk of hospital admission. Patients receive interventions at different times after diagnosis and to avoid immortal time bias I want to differentiate between time before and after patient had intervention. I can calculate the time from diagnosis to intervention (lag time?) for each patient but how do I use this data to construct a time dependent variable. The examples I have seen for time segmented covariates do not seem to address such a situation.

Many thanks
Leonie

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