On 1 Dez., 16:23, Ryan <ryan.andrew.bl...@gmail.com> wrote:
> On Dec 1, 9:15 am, Oliver Kuss <Oliver.K...@medizin.unihalle.de>
> wrote:
>
>
>
>
>
> > On 1 Dez., 11:43, Ryan <ryan.andrew.bl...@gmail.com> wrote:
>
> > > On Dec 1, 2:48 am, Oliver Kuss <Oliver.K...@medizin.unihalle.de>
> > > wrote:
>
> > > > On 1 Dez., 02:16, Ryan <ryan.andrew.bl...@gmail.com> wrote:
>
> > > > > Hi,
>
> > > > > Let me apologize in advance for asking the same question twice. I
> > > > > figured I'd give it another shot.
>
> > > > > Has anyone seen/developed code to run a random effects latent class
> > > > > analysis in SAS. Let's say we have three dichotomous indicator
> > > > > variables (0=No, 1=Yes) that we hypothesize load on a latent class
> > > > > variable (with 3 classes).
>
> > > > > A simple example I just made up: We suspect that there are three
> > > > > classes of people who use illicit substances (class 1 = nonusers/
> > > > > abstainers, class 2 = casual users, class 3 = addicts). Assume we
> > > > > cannot measure directly if someone belongs to any of these classes,
> > > > > but we have 3 indicator variables as indicated previously. Let's also
> > > > > assume that we have two cases per person (measured at equal
> > > > > intervals)...
>
> > > > > //
> > > > > Person Time X1 X2 X3
> > > > > 1 1 0 1 1
> > > > > 1 2 1 0 1
> > > > > 2 1 0 0 0
> > > > > 2 2 0 0 1
> > > > > .
> > > > > .
>
> > > > > N
> > > > > //
>
> > > > > Does anyone know how to construct code (presumably in nlmixed) to run
> > > > > a random intercept LCA and compute the following:
>
> > > > > (1) Probability that a positive response on each item is associated
> > > > > with a particular class
> > > > > (2) Probability that each case is associated with a particular class
> > > > > (3) Any indication that the number of classes we selected does not
> > > > > yield the best fitting model. I assume rerunning the model assuming 2
> > > > > classes, 4 classes, etc. and comparing AICs/BICs might work.
>
> > > > > Any thoughts/recommendations/references would be great.
>
> > > > > Thanks,
>
> > > > > Ryan
>
> > > > Dear Ryan,
> > > > it seems that you also have a longitudinal structure in your data set
> > > > with two (or even more) observations for each person. Then you should
> > > > definitely look at PROC TRAJ (http://www.andrew.cmu.edu/user/bjones/),
> > > > a userwritten SAS prodecure that fits discrete mixture models to
> > > > longitudinal data. I once worked with it and it did fine. Before final
> > > > publication of the results I also coded the model with PROC NLP and it
> > > > yielded the same results. So you might also use PROC NLP or PROC
> > > > NLMIXED for latent class models.
>
> > > > Hope that helps,
> > > > Oliver Hide quoted text 
>
> > > >  Show quoted text 
>
> > > Thanks for responding, Oliver. Thank you for the info about TRAJ
> > > procedure. I would prefer to run the model using the NLMIXED
> > > procedure. I assume it is possible to run such a model as evidenced by
> > > a post by Dale a while back:
>
> > >http://www.listserv.uga.edu/cgibin/wa?A2=ind0503a&L=sasl&D=0&P=26375
>
> > > What's confusing to me about Dale's post is the dependent variable.
> > > What exactly would be the dependent variable in an LCA such as the
> > > example I made up?
>
> > > Ryan Zitierten Text ausblenden 
>
> > >  Zitierten Text anzeigen 
>
> > Dear Ryan,
> > I got your point. I admittedly do not know how such a model can be
> > coded with PROC NLMIXED but I have two more hints which might be
> > useful:
> > 1. There is a SUGI paper using PROC CATMOD (http://www2.sas.com/
> > proceedings/sugi31/20131.pdf) for LCA and 2. There is a userwritten
> > SAS procedure LCA (http://methodology.psu.edu/index.php/downloads/
> > proclcalta) whose first example has four binary indicators which
> > should be grouped in two classes (similar to your problem, without a
> > "response"). Maybe you can use PROC LCA for achieving the results for
> > your data set and then use the description of the model in the PROC
> > LCA handbook for translating the model into PROC NLMIXED.
>
> > Yours,
> > Oliver Hide quoted text 
>
> >  Show quoted text 
>
> Who knew there were so many SAS procedures that could handle an LCA
> model?! I will certainly try to run it (without the REs) using one of
> these other procedures. Regardless, however, if I want to run a random
> effects LCA in SAS, I'm probably going to have to figure out how to do
> it in nlmixed. Thanks again for the info. Ryan Zitierten Text ausblenden 
>
>  Zitierten Text anzeigen 
Dear Ryan,
I'm in a mood today for searching for LCA software ;)))
Give the LCR macro of Diana L. Miglioretti a try (http://
www.grouphealthresearch.org/perpages/migliore/downlds/LCREG2.SAS)
It makes explizit the IML code for fitting the models and maybe is an
even better starting point for coding the model in NLMIXED.
Good luck,
Oliver
