Date: Fri, 29 Jul 2005 17:51:11 -0700
Reply-To: David L Cassell <davidlcassell@MSN.COM>
Sender: "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From: David L Cassell <davidlcassell@MSN.COM>
Subject: Re: Logistic Regression with a Random Effect
Content-Type: text/plain; format=flowed
>I have some binary data on cattle stillbirths (0 or 1) and I am looking to
>do a logistic regression with the data. Some cows have more than one
>calving so I would like to put cow in my model as a random effect.
>Will Proc Logistic accomodate a random effect or would I have to use
>something like Proc Glimmix to get the job done?
First, PROC LOGISTIC won't accomodate that random effect you want.
Second, if your data come from a survey sample with known design
effects, you ought to be looking at using PROC SURVEYLOGISTIC,
which could accomodate the 'cow' effect through clustering in the
Third, if you don't have a survey sample but just observational data,
then PROC GLIMMIX might be the right choice. Or not. It depends
on your data.
How many cows (your independent subjects I assume) do you have?
If you have a large sample of cows, then you could do this using
GEE (Generalized Estimating Equations) through PROC GENMOD. For
a small number of cows, this is not a good choice.
Are you likely to have strong within-subject correlations? Then PROC
GLIMMIX may not be a good choice either. (Dale will corect me if
I'm wrong on this, but I seem to recall this applied to the original
%GLIMMIX macro at least.)
That may leave you with PROC NLMIXED to model your process.
David L. Cassell
3115 NW Norwood Pl.
Corvallis OR 97330
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