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Re: st: Reconcile Log Transformed with Untransformed Results


From   Maarten buis <maartenbuis@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Reconcile Log Transformed with Untransformed Results
Date   Mon, 15 Feb 2010 00:22:00 -0800 (PST)

--- On Sun, 14/2/10, Erasmo Giambona wrote:
> I ran the regressions with both RHS and LHS untransformed
> using both OLS and GLM with link(log). With the OLS the
> coeff on X is 0.006 while with the GLM the coefficient is
> 0.700. I find a bit hard to intepret the GLM coefficient.

Consider the example below:

*--------------- begin example -----------------
sysuse nlsw88, clear
gen byte baseline =1

reg wage grade
glm wage grade baseline,  ///
    link(log) eform nocons
*--------------- end example --------------------


The -regress- results are interpreted as follows:
People without education can expect a wage of
-1.96 dollars an hour (substantively we know that 
people hardly ever pay for the privelege to work,
so this is a sign of bad model fit), and they get
74 cents an hour more of every additional year of 
education.

The -glm- results are interpreted as follows:
People without education can expect a wage of 
2.25 dollars an hour, and for every additional
year of education they can expect an increase 
of 9.7%.

Hope this helps,
Maarten

--------------------------
Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
Germany

http://www.maartenbuis.nl
--------------------------


      

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