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st: Estimation of differences of logistic regression models in three groups


From   roland andersson <rolandersson@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Estimation of differences of logistic regression models in three groups
Date   Fri, 20 Feb 2009 13:47:02 +0100

I am analysing the frequency of surgical complicationafter
laparoscopic compared to open appendectomy in alrge national sample of
patients.

I use logistic regression to adjust for differences in comorbidity,
age and sex between the two surgical methods. I obtain a higher risk
of complications after laparoscopic appendectomy ( OR 1.97).

I know want to analyse if this risk-difference between laparoscopic
and open appendectomy has decreased between three timeperiod, and
between three geographical regions.

Shall I put the timeperiods and regions in the same model and use some
postestimation method to do the inference? Or shall I do separate
calculations for each timeperiod and geographic region? If so how can
I estimate the difference in risk between the timepriods and make the
statistical inference?

Here is a simplified model with the important variables:

xi:logistic perpostkirkomplik lapscopi i.appdgn  i.agekat sex i.period
i.region comrbidityvariables, or

I assume this can be done with some postestimation methods but I need
your helpt o understand them.

Roland Andersson
Jönköping, sweden

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