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st: Survival Analysis


From   "Luciana Lopes" <lucilopes@terra.com.br>
To   "statalist" <statalist@hsphsun2.harvard.edu>
Subject   st: Survival Analysis
Date   Thu, 8 May 2008 11:09:25 -0200

Hello,
           I have a dataset with multiple spells (failures) per subject. There are left-censored, right-censored, left-truncated and right-truncated spells.
           I would like to run a semi parametric Cox model with a Gamma shared frailty component and a time-varying covariate. I think that the proportional hazards assumption is violated for a model with frailty and/or time-varying covariates. What I think is true? Is it a problem when the proportional hazards assumption is violated for this model?  
            If the proportional hazards assumption is violated and the left-censored and left-truncated spells are discarded, will I have biased results about the shape of the hazard function?
 
Thanks a lot
Luciana            



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