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st: RE: psmatch2 and stcox


From   "Villa Lora, Juan Miguel" <juanmiguelv@iadb.org>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   st: RE: psmatch2 and stcox
Date   Thu, 12 Nov 2009 09:23:48 -0500

Hi!
I've got suggestions:
1. Try to estimate the propensity score firstly (with a probit or logit) and set the prediction in the option p(your_prediction). This saves you time when running the command several times. 
2. Specify the option "noreplacement" which yields a 1-1 matching as wanted. 

JM.

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of moleps islon
Sent: Martes, 10 de Noviembre de 2009 03:28 p.m.
To: statalist@hsphsun2.harvard.edu
Subject: st: psmatch2 and stcox

I´m trying to match 336 exposed patients from a cohort with a total of
966 patients using psmatch2:

xi:psmatch2 E `var', outcome(out) neighbor(1) common

I thought this would give me 1:1 matching, but I get 336 exposed and
662 control patients.

Then doing

ttest -different variables-, by(_t)

doesnt really match very well despite reasonable overlapping propensity distributions. Is this due to omitting the weighting option?

I´d like to use these propensity matched data for a logrank test, but I´m uncertain to the type of weight I should use. I assumed it should be pweight, but I found another posting here where they said fweight leaving me uncertain....

Regards

M

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