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RE: st: ROC with complex data sets


From   "Taylor, Sharonda A." <sataylor@TexasChildrensHospital.org>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: ROC with complex data sets
Date   Tue, 21 Aug 2007 09:48:43 -0500

Steven, 
Thanks for the input. The problem is that I cannot simply convert pweights to frequency weights  by rounding. They are derived at in very different ways. Even with using svyset, I cannot run ROC because it does not take into account the complex design or the pweights. Any other suggestions? Am I doomed to hand calculate this?
 
Sharonda Alston Taylor, MD
Adolescent Medicine Fellow
Department of Pediatrics
Section of Adolescent Medicine & Sports Medicine
Baylor College of Medicine
Texas Children's Hospital
(O) 832-822-0612 

________________________________

From: owner-statalist@hsphsun2.harvard.edu on behalf of Steven Joel Hirsch Samuels
Sent: Mon 8/20/2007 11:02 AM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: ROC with complex data sets



Sharonda:

Short answer to your question:
Round the pweight variable to the nearest integer and use the 
resulting variable as an "fweight".

Long answer: The ROC programs will not take into account other 
aspects of the survey (stratification, clustering, multiple stages). 
Therefore confidence intervals and p-values quoted in the output will 
be wrong.  Also, the  ROC analysis will not be much good if your 
model is not good: so you are still obligated to build a good model 
and check its fit. For example, if there are strong interactions, you 
should include them in your model.  Use Stata's survey features:  -
svyset- your data and build your model with Stata's -svy- logistic 
command.  You may also want to learn about Stata's -zinb- command, 
which can demonstrate failure of the ordinary logistic model.

Read the survey documentation to understand how the weighting was 
done.  If any part of the weighting or stratification involved your 
outcome variable, you should probably run an unweighted analysis.

-Steven





On Aug 20, 2007, at 8:34 AM, Taylor, Sharonda A. wrote:
>
> I am very new to research. I am attempting to do ROC analysis using 
> a complex survey that uses pweights. Stata 9.2 uses frequency 
> weights. I understand that pweights and fweights are not 
> interchangeable. Are there any downloads that will allow me to run 
> the analysis with the pweights? Please advise.


sjhsamuels@earthlink.net
18 Cantine's Island
Saugerties, NY 12477
Phone: 845-246-0774
EFax: 208-498-7441




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