Date: Tue, 20 Dec 2005 15:16:58 -0800
Reply-To: David L Cassell <davidlcassell@MSN.COM>
Sender: "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From: David L Cassell <davidlcassell@MSN.COM>
Subject: Re: Cox model assumption check
Content-Type: text/plain; format=flowed
>I need to check the assumption of Cox model for the treatment group,
>which is the main variable of interest, and there are also quite a lot
>covariates in the data set. The follow-up time (survival time) is days
>from randomization to either diagnosis of disease or censoring.
>Is there a way that I can perform this assumption check in SAS? I
>thought I can do a plot of residual of survivial time against time?
>Will this work?
>I appreciate any input from you folks!!!
Before I get to PROC PHREG, I usually check the proportional hazards
using PROC LIFETEST.
If the proportional hazards assumptionl is appropriate, then the estimates
log(-log(estimated survival distribution)) plotted against the log(TIME)
should be parallel lines.
If the Weibull model is a good fit, then these lines should be pretty
If you have SAS 9.1 then you can plot this out using ODS Statistical
David L. Cassell
3115 NW Norwood Pl.
Corvallis OR 97330
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