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st: Survival with time varying covariates


From   n p <nik_padazis@yahoo.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Survival with time varying covariates
Date   Thu, 31 Jul 2003 04:29:07 -0700 (PDT)

Hi Stata users,

I need your help in the following problem. I want to
perform a survival analysis (via Cox PH models) where
some covariates (e.g. demographics) are constant over
study time while others (Marker1 and Marker2) are
periodically measured  (usually after time zero and
not simultaneously). Thus I have 3 datasets 

a) 1 record per subject, with time of event or
censoring and other not time varying covariates
b) n1 records per subject for repeated measurements of
marker1 (time and value of measurement)
c) n2 records per subject for repeated measurements of
marker2 (time and value of measurement)

The effect of both markers on the hazard is the main
question in this study.

I checked the manual's example "Stanford heart
transplant data" and the "stsplit" command. I also
checked "stegen" and "stcoxtvc" using "findit time
varying covariates" but I am still puzzled with this.
Is there an easy way to prepare the data at least for
one of the two markers? How can I deal with the
unknown markers' values between time zero and their
first measurement?

I am using Stata 7 on a 2.4 GHz 512 RAM WinXP machine.

Thanks in advance for any help.

Nikos Pantazis
Biostatistician


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