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st: interpretting log transformed co-efficients


From   Ashwin Ananthakrishnan <ashwinna@yahoo.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: interpretting log transformed co-efficients
Date   Sun, 8 Feb 2009 08:34:52 -0800 (PST)

Hi, 

I'm having some trouble interpretting the linear regression co-efficients for log transformed variables. 

I have outcomes (such as length of stay or costs) that are not normally distributed, so I'm including the log transformed (now normal) variables as the outcome measures in linear regression models. 

But I'm not really sure how to interpret the resulting co-efficients. Do they represent a % change in outcome for a defined change in a predictor variable? 

Just for example, suppose I'm modelling length of stay against gender (male 0 female 1). 

Without log transformation, if I get a linear regression co-efficient of 0.6, I can say that females have a 0.6 days longer stay. 

But if I use log (length of stay) as the outcome and get a co-efficient 0.2 for the same linear regression model, how do I interpret this? 

Thanks. 


      
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