Date:         Tue, 19 May 2009 08:35:30 -0700
Reply-To:     elodie <elodie.gillain@GMAIL.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         elodie <elodie.gillain@GMAIL.COM>
Organization: http://groups.google.com
Subject:      Re: glimmix question
Comments: To: sas-l@uga.edu
Content-Type: text/plain; charset=ISO-8859-1

On May 19, 9:37 am, rh...@UNMC.EDU (Robin R High) wrote:
> For the record, I hastily typed in the incorrect formula for the
> cumulative probabilities yesterday for the cumulative logit model, so the
> "modified" version based on the printed intercepts below (if I copied them
> correctly) should be:
>
>                     Cumulative Probs              Individual probs add to
> 1
> row 1: EXP(-3.6743)/(1+EXP(-3.6743)) = 0.02474   prob A = .02474 = 0.02474
> row 2: EXP(-2.3303)/(1+EXP(-2.3303)) = 0.08864   prob B = .08864 - .02474
> = 0.06390
> row 3                                  1         prob C =  1     - .08864
> = 0.91136
>
> The ILINK option gives the cumulative probs for all but the last level --
> the individual ones can be computed as shown above.
>
> Robin High
> UNMC
>
> elodie <elodie.gill...@GMAIL.COM>
> Sent by: "SAS(r) Discussion" <SA...@LISTSERV.UGA.EDU>
> 05/18/2009 09:00 AM
> Please respond to
> elodie <elodie.gill...@GMAIL.COM>
>
> To
> SA...@LISTSERV.UGA.EDU
> cc
>
> Subject
> glimmix question
>
> Hi all,
>
> I am running a generalized regression. The dependent variable has 3
> categories.
>
> The syntax I am using is
>
> proc glimmix data=;
> class timeclass ;
> model dependent var categorized =  / solution ;
> random intercept  / subject=id;
> run;
>
> The output reads:
>   The GLIMMIX procedure is modeling the probabilities of levels of
> the dep variable having lower Ordered Values.
>
> Effect       dep var categorized    Estimate
>
> Intercept    1               -3.6743
> Intercept    2               -2.3303
>
> I am confused about what those two intercepts mean. I think that if I
> take the exponential of intercept 1, I get an odds ratio. But I do not
> know whether it measures the odds ratio of going from category 2 to
> category 1, or from category 3 to category 1, or some other
> transition. The manual of proc glimmix leaves much to be desired. Any
> ideas?
>
> Thanks a lot for the help.

Thank you so much for your messages. I very much appreciate your help.
You are right, glimmix is a difficult procedure to use, and I need
more practice with genmod, logistic and the more basic procs. The
ILINK option is useful for getting the estimated probabillities,
thanks.

I have another question. When I include a (0-1) binary covariate to
the model of my original post, I get a (small but significant)
negative coefficient. I will denote the coefficient beta. For some
reason, I do not get an odds ratio when I ask for it. This is
confusing.

So I do not know how to interpret that negative coefficient. Should I
interpret beta using the following equation
exp(\beta) = \frac{P(Y=B|X=1)/P(Y=A|X=1)}{P(Y=B|X=0)/P(Y=A|X=0)}?
or maybe
exp(\beta) = \frac{P(Y=C|X=1)/P(Y=A|X=1)}{P(Y=C|X=0)/P(Y=A|X=0)}
Any ideas?

Thanks a lot for your help