Re: st: compare effect size between dummys and metrics variables in logistic regression

[Morten Hesse <mh@crf.au.dk>]

Hi
I am a newbie, but I get confused about this. It may well be that 
Michael is right. But if I conduct a logstic regression, and then write:

test [continuous covariate]=[1.dichomotomous covariate]

Then I get a chi-square statistic (with one df) and a p-value. It looks 
just like any other result of "test":

 ( 1)  [dep var]cont_covar - [dep var]1.dic_covar = 0

           chi2(  1) =    4.28
         Prob > chi2 =    0.0387

In my understanding, this asks the question "is the difference between 
the value of the coefficient when dic_covar=1 significantly different 
from the coefficient of cont_covar.

If this does not make sense, then why does STATA do it? Is this not what 
Joerg would want to use?

Greetings
Morten

Den 27-09-2010 09:21, Michael N. Mitchell skrev:
> Greetings Joerg
>
>   If you were doing an OLS regression, I would say that you could 
> report the partial (or semi-partial) correlation associated with each 
> of the variables. However, as you note, you are using binary logistic 
> regression. While you could technically create z scores for the binary 
> variables to try and put them on the same scale as the z-transformed 
> variables, those results would not make much sense. You could take the 
> z-transformed variables and convert them into 0/1 variables by cutting 
> them into two arbitrary groups, but that would not make much sense. My 
> thoughts are that there is not much you can do to compare the "apples" 
> and "oranges" here in terms of the effect size.
>
> Best regards,
>
> Michael N. Mitchell
> Data Management Using Stata      - 
> http://www.stata.com/bookstore/dmus.html
> A Visual Guide to Stata Graphics - 
> http://www.stata.com/bookstore/vgsg.html
> Stata tidbit of the week         - http://www.MichaelNormanMitchell.com
>
>
>
> On 2010-09-26 11.23 AM, Jörg Eulenberger wrote:
> > Dear Statalisters,
> > a have an more statistical Question. I want to calculate an binary 
> > logistic regression. I
> > have all metric variables z-transformed (mean = 0, std=1) to compare 
> > the effect size
> > between the independent variable. But I have also dummys in my 
> > Regressionmodell. What can
> > i do to compare the effect size of the dummy's with the effect size 
> > of the metric
> > independent variables? Or is that completely impossible?
> > Thanks,
> > Joerg
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