[R] coefficient of logistic regression

[John Fox]

Dear Ahmet,

Sorry for the slow response, but I've been busy all today, coincidentally 
teaching a workshop on logistic regression.

Tom Blackwell sent you a useful suggestion for interpreting coefficients on 
the odds scale. If you want to trace out the partial relationship of the 
fitted probability of response to a particular predictor holding others 
constant, you can set the other predictors to typical values and let the 
predictor in question vary over its range, transforming the fitted log-odds 
to the probability scale.

You may be interested in my effects package (on CRAN or at 
<http://socserv.socsci.mcmaster.ca/jfox/Misc/effects/index.html>), which 
makes these kinds of displays for linear and generalized-linear models, 
including those with interactions.

Regards,
  John

At 03:06 PM 6/3/2003 +0300, orkun wrote:
>John Fox wrote:
>
>>At 11:54 AM 6/3/2003 +0300, orkun wrote:
>>
>>>in logistic regression,
>>>I want to know that it is possible to get probability values of each 
>>>predictors by
>>>using following formula for each predictor one by one (keeping constant 
>>>the others)
>>><<< exp(coef)/(1+exp(coef)) >>>
>>
>>
>>Dear Ahmet,
>>
>>This will almost surely give you nonsense, since it produces a fitted 
>>probability ignoring the constant in the model (assuming that there is 
>>one), setting other predictors to 0 and the predictor in question to 1. 
>>What is it that you want to do?
>>
>>I hope that this helps,
>>  John
>>
>>
>thank you
>
>Say, I just want to find each predictor's particular effect on dependent 
>variables.
>Actual model is to prepare landslide susceptibility map on GIS. So  I want 
>to know
>what the effect as probability value comes from each predictor. For 
>instane what is the effect
>of  slope on landslide susceptibility. Should I keep others constant ?
>
>kind regards




-----------------------------------------------------
John Fox
Department of Sociology
McMaster University
Hamilton, Ontario, Canada L8S 4M4
email: jfox at mcmaster.ca
phone: 905-525-9140x23604
web: www.socsci.mcmaster.ca/jfox