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st: survival analysis: stratifying and adjusting for leadtime


From   Michael McCulloch <mm@pinest.org>
To   Statalist <statalist@hsphsun2.harvard.edu>
Subject   st: survival analysis: stratifying and adjusting for leadtime
Date   Thu, 15 Nov 2007 21:49:55 -0800

Dear Statalist members,
I am comparing two groups for survival after treatment, A and B, and am not sure how to specify the -sts graph- or -stcox- statements for subgroups of leadtime.

In group A, "exposed", the leadtime between diagnosis and treatment varied considerably (from 0 to 123 days, with median of 31 days).

In group B, "unexposed", leadtime is not relevant, and is thus missing for all observations.

When I compare survival between the two groups with Kaplan Meier, I'd like to stratify on values of leadtime for group A, which is 0-30 days, 30-60 days, and 60-90 days. How can I specify the following command to reflect those 3 levels of leadtime?
sts graph, by(group)

When I compare survival with Cox regression, I'd like to adjust for levels of leadtime. How can I specify the following command to reflect those 3 levels of leadtime?
stcox treatment, by(group)

Thank you kindly.

--

Michael McCulloch
Pine Street Foundation
124 Pine St., San Anselmo, CA 94960-2674
Tel: (415) 407-1357
Fax: (415) 485-1065
mcculloch@pinestreetfoundation.org
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