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re: st: Using AIPW for missing data purposes in RCTs?


From   "Ariel Linden, DrPH" <ariel.linden@gmail.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   re: st: Using AIPW for missing data purposes in RCTs?
Date   Wed, 26 Jun 2013 10:22:20 -0400

I am perplexed by your issue here. Why would you use adjustment strategies
in an RCT? That is, unless your randomization failed? If so, you've got all
sorts of other problems on your hands...

As for adjusting for missing data, I am not sure what you are specifically
referring to? Missing data on patient characteristics, outcomes, censoring,
what? Are you planning on analyzing your data longitudinally or as a point
treatment study? If you do not describe your problem in sufficient detail,
no one will be able to give you a helpful response.

Missing data can be imputed via Stata's -mi- suite of commands, if that
makes sense in your particular situation.

As for IPTW and missing data, you are only partially correct. In the
literature (particularly James Robins work) the reference to missing data
involves handling of censoring. In short, there are two weights that are
generated, (1) the weight based on the propensity score to model probability
of receiving treatment, and (2) the weight based on the probability of being
censored. The two weights are then combined.

There is a Stata Journal paper that came out a few years ago that shows how
to perform this manually. 

Fewell Z  et al. Controlling for time-dependent confounding using marginal
structural models. Stata Journal 2004;4( 4): 402-420.

I hope this helps

Ariel

Date: Tue, 25 Jun 2013 12:17:34 +0000
From: "Stephen Kay (TRUELIFE)" <Stephen.Kay@completetruelife.com>
Subject: st: Using AIPW for missing data purposes in RCTs?

Hello,

Stata 13 has augmented inverse probability weighting, AIPW, capabilities
aimed at observational data. I don't have Stata 13 so cannot test it out.
Does anyone know if it can be used/modified  for missing data problems in
RCTs (which is one area that AIPW is used for)? I have such a trial to
analysis and it may be worth upgrading if so. Or can anyone point me to
other ado files for Stata 12 that can do so?

Many thanks,

Steve 


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