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st: regression assumption question

From   moleps islon <>
Subject   st: regression assumption question
Date   Mon, 9 Mar 2009 19:49:06 +0100

Dear listers,
I've got data on 300 patients preop and postop using the VAS scale
(ordinal scale). I'm trying to locate factors predicting improvement
postop. However there are several questions pertaining to this that
I'm unsure of. 1)Do I violate the assumption of independence? I assume
there would be some correlation between preop and postop within the
patients. 2)Would you recommend using delta (preop-postop) as the
dependent variable or postop alone? The analyses so far show some
heteroscedasticity-in case i violate the independence assumption- is
it possible to do add both vce(robust) and vce(cluster id) ?

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