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st: understanding the -asis()- option in -stsplit-


From   "Jesper Lindhardsen" <JESLIN01@geh.regionh.dk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: understanding the -asis()- option in -stsplit-
Date   Fri, 18 Nov 2011 10:50:13 +0100

Hi All,

This may be simple, but I am having a hard time with a futher split
(-stsplit-) of multiepisode survival data (Stata 11.2/MP on windows
server).
Basically I want to split some of the observations within an individual,
if exposed, into several new observations. However, this (I figure)
causes the offset (-after()- option) to vary within individuals, which
forces the use of the -asis()- option-. But I cannot figure out the
proper use, and the documentation on this option is scarse.

In the below very simplified example, I want to split the episodes with
changevar==1 to be further divided in two, however, this does not work
(only one of two episode is splitted).
I've tried several other stsplit commands, but no succes. 



clear all

input time	id	changevar	event

30	1	.	0

40	1	1	0

50	1	.	0

60	1	1	0
			
end

stset time, id(id) f(event)

stsplit hej if changevar==1,at(2) after(time=asis(_t0))

sort time


Hope you can help, 

Jesper


Jesper Lindhardsen
MD, PhD candidate
Department of Cardiovascular Research
Copenhagen University Hospital, Gentofte
Denmark


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