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Re: st: ROC with complex data sets


From   Steven Joel Hirsch Samuels <sjhsamuels@earthlink.net>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: ROC with complex data sets
Date   Tue, 21 Aug 2007 14:05:02 -0400

Sharonda,

I believe you are mistaken.

Although the weighting computations may be complicated, all probability surveys wind up with a "final" weight variable; call it "final_wt". It is the one that would be designated the probability weight in -svyset- , via "[pweight=final_wt]", and it is the one you would round to create a frequency weight. If that final weight variable is not present in your data, then contact the survey developers or the documentation for advice on how to calculate it.

Stratification and clustering will not affect the computation of sensitivity and specificity and, by extension, the ROC curves. Only the p-values, standard errors, and C.I.'s will be incorrect.

Note: There can be many "final weights" in a survey data set. but only one will be used at a time. In the 1999-2000 National Health And Nutrition Examination Survey, for example, there were exam weights, interview Weights, and a variety of weights for analyses of chemicals that were measured only in sub-samples. Problems do arise for investigators who want to analyse the association of two chemicals not always measured together.

Steven

On Aug 21, 2007, at 10:48 AM, Taylor, Sharonda A. wrote:


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?

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.
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