Date:         Thu, 7 Jul 2005 18:06:39 -0400
Reply-To:     Manon Girard <mansof@VIDEOTRON.CA>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Manon Girard <mansof@VIDEOTRON.CA>
Subject:      Proportion in Logistic regression
Content-Type: text/plain; charset=US-ASCII

Hello members,

I am stuck in a basic problem.

My response variable is a proportion (A/B) and I have to modelized it in a
logistic regression, then I have to estimate the treatment effects using
predicted percents from the model.

It my proc below would do it ?

proc logistic data=xxx;
  class trt_grp covariates;
  model A/B=trt_grp covariates;
  output out=x predicted=p;
run;

When I tested it with my knowledge of logistic regression, I assumed that
with the intercept only, this should come as the same proportion of the
actual proportion.
As an example, if I use a 0/1 response variable (say C), a proc like "model
C=;", would give an estimated proportion as being the same as the proportion
of 0/1 in my dataset.

I followed this strategy but this doesn't seem to work this way.

If I put the question in another way, I calculated "result=A/B" for each
individual in my dataset. I want to see if there is a treatment effect in
"result", while taking into account all the possible covariate. Is Logistic
the best way to do such analysis ?

Thanks
Manon