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st: How to "reverse" log transformated result


From   Morten Støver <morten.stover@ntnu.no>
To   statalist@hsphsun2.harvard.edu
Subject   st: How to "reverse" log transformated result
Date   Wed, 28 Sep 2011 09:40:39 +0200

I'm doing an multilevel linear regression analysis where I try to investigate if there are variation in the lenght of the rehabilitation process before people are being granted a disability pension. I measure this in days, and since my data are very skewed, I've done a log transformation. Now I wonder how I can transform the results back to the original scale of measurement. As an example, this are the results for the different types of diagnosis.
"Other" diagnosis:    (ref)
Mental disorders:    0.1993938
Musulosceletal:        0.0840664

If I now try to transform the data back using di exp(.1993938) I get the result 1.2206626. If I try to analyse the data without log transforming them, I find that the mental disorders group have 166 days (95% CI: 75.5-265.6) longer rehabilitation time before being granted a disability pension than the "other" diagnosis group. I guess that the di exp is not the right way to transform the results back, but I don't know any other way to do it.
I'm using Stata 11.
Thank you for your help


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