Re: st: OR results of mhodds vs. logistic

[Suzy <scott_788@wowway.com>]

Sorry, I sent the incorrect output in the previous e-mail -  the 
question and correct output are below:

Dear Statalisters:
I think this might be more of a statistical question rather than a Stata 
question. I would like to know why the  odds ratio estimate, as an 
approximation to the odds ratio
for a one unit increase in x1 (x1 is continuous) for the mhodds command  
is so different than the logistic output from the command below.  FYI, 
x2 is continuous as well. Both x1 and x2 are linear in the logit.
Suzy


OR results for x1 controlling for x2 are different for the mhodds 
command and the logistic command below:


mhodds Y x1 x2(x2 is controlled)  by(x3)

-------------------------------------------------------------------------------
    Y    | Odds Ratio        chi2(1)         P>chi2       [95% Conf. 
Interval]
----------+--------------------------------------------------------------------
       1 |   1.154021          21.50         0.0000         1.08622    
1.22606
       2 |   1.095894           5.87         0.0154         1.01764    
1.18017
       3 |   1.073977           3.63         0.0566         0.99799    
1.15574
       4 |   1.308015           5.38         0.0203         1.04258    
1.64103
       5 |   1.004919           0.00         0.9552         0.84669    
1.19271
-------------------------------------------------------------------------------

 
by x3, sort : logistic dmcat x1 x2

> x3 = 1


------------------------------------------------------------------------------
      Y     | Odds Ratio   Std. Err.      z    P>|z|     [95% Conf. 
Interval]
-------------+----------------------------------------------------------------
        x1  |   1.18209    .039921      4.95   0.000      1.10638    
1.262982
        x2  |   1.051794   .0060071     8.84   0.000     1.040086    
1.063634
------------------------------------------------------------------------------

------------------------------------------------------------------------------
-> x3 = 2

------------------------------------------------------------------------------
      Y     | Odds Ratio   Std. Err.      z    P>|z|     [95% Conf. 
Interval]
-------------+----------------------------------------------------------------
        x1  |   1.119092   .0440137     2.86   0.004     1.036067    
1.208769
        x2  |   1.063327   .0077098     8.47   0.000     1.048323    
1.078546
------------------------------------------------------------------------------

------------------------------------------------------------------------------
-> x3 = 3


------------------------------------------------------------------------------
      Y     | Odds Ratio   Std. Err.      z    P>|z|     [95% Conf. 
Interval]
-------------+----------------------------------------------------------------
        x1  |   1.110412   .0408657     2.85   0.004     1.033137    
1.193467
        x2  |   1.068197   .0067078    10.51   0.000     1.055131    
1.081426
------------------------------------------------------------------------------

------------------------------------------------------------------------------
-> x3 = 4

------------------------------------------------------------------------------
      Y     | Odds Ratio   Std. Err.      z    P>|z|     [95% Conf. 
Interval]
-------------+----------------------------------------------------------------
        x1  |   1.211418   .1138217     2.04   0.041     1.007668    
1.456367
        x2  |    1.05441   .0171186     3.26   0.001     1.021387    
1.088502
------------------------------------------------------------------------------

------------------------------------------------------------------------------
-> x3 = 5

------------------------------------------------------------------------------
      Y     | Odds Ratio   Std. Err.      z    P>|z|     [95% Conf. 
Interval]
-------------+----------------------------------------------------------------
        x1  |   1.007958   .0746672     0.11   0.915     .8717407     
1.16546
        x2  |   1.045343   .0116738     3.97   0.000     1.022711    
1.068475
------------------------------------------------------------------------------





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