Date: Sun, 25 Dec 2011 21:27:37 -0800
Reply-To: zmlr <jgz02865@HOTMAIL.COM>
Sender: "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From: zmlr <jgz02865@HOTMAIL.COM>
Subject: Problem of COX model with time dependent covariate
Content-Type: text/plain; charset=us-ascii
Hi all,
I am trying to detect association between a covariate and a disease outcome.
This covariate shows time-varying effect, so I use "Cox w/Time-Dep cov" in
SPSS 17.0 to build cox model, the T_COV_ is equal to T_. The result is as
follows:
B SE Wald df Sig. Exp(B)
eGFR_BASE -13.603 .548 616.007 1 .000 .000
T_COV_*eGFR_BASE .860 .115 55.859 1 .000 2.362
Some materials explained that "T_COV_*eGFR_BASE" is a time-covariate
interaction item in fact, so I recode a new variable,named "TIME", which
exactly equal to survival time, then input the conventional Cox model. The
result is as follows:
B SE Wald df Sig. Exp(B)
eGFR_BASE 6.317 .370 291.547 1 .000 554.166
TIME*eGFR_BASE -3.372 .076 1944.385 1 .000 .034
My Questions are:
1, Why it's so different between two results? How T_COV_ was calculated in
SPSS, and is it the same with the survival time?
2, I also try to calculate it using Cox in R, I use time:eGFR_BASE as time
dependent item, the result is same as the second one above.But whether I can
do the first procedure in R?
Many thanks,
Kevin
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