st: survival analysis: stratifying and adjusting for leadtime

[Michael McCulloch <mm@pinest.org>]

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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