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st: KM curve adjusted by the Inverse Probability of Treatment Weights(IPTW)


From   Marcos Vinicius <bioestatistico@inbox.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: KM curve adjusted by the Inverse Probability of Treatment Weights(IPTW)
Date   Thu, 20 Dec 2012 08:55:11 -0800

Hello,
I would like to generate a Kaplan Meier curve adjusted(controlled/corrected) by the Inverse Probability of Treatment Weights(IPTW).
Supose I have a dataset with columns: tx=treatment (0/1)  , ps=propensity score weig=  Inverse Probability of Treatment Weights (iptw),time (=survival time)remission(1/0) (0=censored),
In IPTW, individuals are weighted by the inverse probability of receiving the treatment that they actually received.
In SAS I tried this code but it is not working although it is indicated in the SAS/STAT
12.1 User’s Guide The LIFETEST Procedure (Chapter)
Someone could help me with a Stata code to produte and compare 2 Km curves according to treatment group but adjusted by iptw(weig)
proc lifetest method=km data=ps plots = (survival );
 
time time*remission(0);
 weight weig;
survival out=surv_data conftype=loglog ;
/*weight weig;*/
ODS EXCLUDE ProductLimitEstimates Means LogrankHomCov WILHOMCOV HomStats TaroneHomCov PetoHomCov Rank HomTests  ;
/*weight weig;*/
strata tx;
/*weight weig;*/
 run;
[
Error message from SAS log
ERROR 180-322: Statement is not valid or it is used out of
               proper order.


After program the  propensity score weight , also referred to as the inverse probability oftreatment weight (IPTW)( weig in the  SAS code) I tried to use the weight statatement from proc Lifetest to produce a Kaplan-Meier curve adjusted by iptw. It is not working.
Someone could help me in the code implementation  or guide another way to produce the KM curve adjusted by propensity score?:
Many thanks,
Vinicius.

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