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st: RE: regression using eform


From   "Kieran McCaul" <Kieran.McCaul@uwa.edu.au>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: regression using eform
Date   Fri, 4 Sep 2009 05:15:58 +0800

...

I agree with Clive's comment regarding the use of step-wise regression.

More to the point, however, why do you think that exponentiating the
coefficients from a linear regression will give you odds ratios?

______________________________________________
Kieran McCaul MPH PhD
WA Centre for Health & Ageing (M573)
University of Western Australia
Level 6, Ainslie House
48 Murray St
Perth 6000
Phone: (08) 9224-2701
Fax: (08) 9224 8009
email: Kieran.McCaul@uwa.edu.au
http://myprofile.cos.com/mccaul 
http://www.researcherid.com/rid/B-8751-2008
______________________________________________
If you live to be one hundred, you've got it made.
Very few people die past that age - George Burns

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Tina
Hernandez-Boussard
Sent: Friday, 4 September 2009 1:54 AM
To: statalist@hsphsun2.harvard.edu
Subject: st: regression using eform

Hi,

I have a question regarding a regression model that I am running.  I  
am looking at predictors for a variable slope, which is growth of a  
tumor per day.  I have ran this model and using

sw, pr(.2):regress slope smoker exercise bmi , eform(odds)

I have reran the model, only multiplying the slope by 365.25 to get  
the growth per year.  I did not think that this would change  
anything, yet it changes the odds ratios.  I still get the same  
prob>f, r-squared, and adjusted r-squared.  However, model and  
residual ss, df, and ms are different.

Can someone please explain why my odds ratios are changing, yet the t  
and P>|t| are not?

First model:
------------------------------------------------------------------------

---
        slope |       odds   Std. Err.      t    P>|t|     [95% Conf.  
Interval]
------------- 
+----------------------------------------------------------------
     exercise |   1.000341   .0001396     2.45   0.017      
1.000062     1.00062
          bmi |   .9999843   9.47e-06    -1.66   0.102     . 
9999653    1.000003
       smoker |   1.000748   .0003167     2.36   0.021      
1.000116    1.001382

Model with slope*365.25:

------------------------------------------------------------------------

------
       growth |       odds   Std. Err.      t    P>|t|     [95% Conf.  
Interval]
------------- 
+----------------------------------------------------------------
    exercise  |   1.132765   .0577325     2.45   0.017      
1.023043    1.254254
          bmi |   .9942751   .0034406    -1.66   0.102     . 
9874212    1.001177
       smoker |   1.314259   .1519301     2.36   0.021      
1.043092    1.655921


Thanks,

Tina 
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