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
In-Reply-To:  <200512201450.jBKBk8u1012059@mailgw.cc.uga.edu>
Content-Type: text/plain; format=flowed

statsas@GMAIL.COM wrote:
>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
assumption
using PROC LIFETEST.

If the proportional hazards assumptionl is appropriate, then the estimates
of the
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
straight too.
If you have SAS 9.1 then you can plot this out using ODS Statistical
Graphics.

HTH,
David
--
David L. Cassell
mathematical statistician
Design Pathways
3115 NW Norwood Pl.
Corvallis OR 97330

_________________________________________________________________
Express yourself instantly with MSN Messenger! Download today - it's FREE!
http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/