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st: Model in outdated time varying cox command with longitudinal data


From   Deepa Aggarwal <da.aggarwal@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Model in outdated time varying cox command with longitudinal data
Date   Thu, 9 Apr 2009 19:14:12 -0400

Hi All,

I am using Cox command of Stata for the longitudinal analysis in time
varying  cox regression. My data looks like following data:

Id     d_entry           d_censor         status          age       x2
1      20jan2008     22jan 2008        0               62          0
1      22jan 2008    24jan 2008        0               62          0
1      24jan 2008    26jan 2008        0               62          1
1      26jan 2008    28jan 2008        1                62          0
2      13jan 2008    18jan 2008        0               70           0
1      18jan 2008    20jan 2008        0               70           1
1      20jan 2008    24jan 2008        0               70           0
1      24jan 2008    26jan 2008        1                70          1

Here id is patient id number, d_entry is the date of entry,  d_censor
is the date of censoring, status is the censoring variable, age is
fixed for each id, x2 changes with time for each id.

To use time varying Cox regression first I used stset command. Then I
used the following command which treats x2 as a time varying
covariate.
Cox  date_censor  age x2, dead(status)  tvid(id) hr

Now my question is:

 What will be the model if I use this command? For example is it

Log h(t) = log h0(t) + b1 *age + b2* x2*t

I know it is an outdated command. I am a new stata user. I searched a
lot to understand this command, but everywhere I can get details for
stcox not for cox.

Thanks for your consideration.

Deepa
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