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st: RE: How to "reverse" log transformated result


From   "Jesper Lindhardsen" <JESLIN01@geh.regionh.dk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: How to "reverse" log transformated result
Date   Wed, 28 Sep 2011 13:14:57 +0200

Hi Morten,

I may have misunderstood, but as you do not provide your syntax and/or exact regression method, it is hard to know.
My guess is that the first result is a ratio from comparing groups, while the other result could be an estimate at the mean values in the two groups.
As Nick suggested the rate of being granted a disability pension, may be easier to model.

Just my thoughts,

Jesper


-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Morten Støver
Sent: 28 September 2011 09:41
To: statalist@hsphsun2.harvard.edu
Subject: st: How to "reverse" log transformated result

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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