[R] question on multilevel modeling
Christoph Buser
buser at stat.math.ethz.ch
Tue Nov 7 08:59:26 CET 2006
Dear Christine
I think the problem in your second model is that you are
including "CORUMTO" both as a fixed effect and as a random
effect.
Regards,
Christoph
--------------------------------------------------------------
Credit and Surety PML study: visit our web page www.cs-pml.org
--------------------------------------------------------------
Christoph Buser <buser at stat.math.ethz.ch>
Seminar fuer Statistik, LEO C13
ETH Zurich 8092 Zurich SWITZERLAND
phone: x-41-44-632-4673 fax: 632-1228
http://stat.ethz.ch/~buser/
--------------------------------------------------------------
Christine A. Calmes writes:
> Hi,
>
> I am trying to run a multilevel model with time nested in people and
> people nested in dyads (3 levels of nesting) by initially running a
> series of models to test whether the slope/intercept should be fixed or
> random. The problem that I am experiencing appears to arise between the
> random intercept, fixed slope equation AND.
>
> (syntax:
> rint<-lme(BDIAFTER~BDI+WEEK+CORUMTO, random=~1|DYADID/PARTICIP,
> data=new)
> summary(rint))
>
> the random slope, random intercept model
>
> (syntax:
> rslint<-lme(BDIAFTER~BDI+WEEK+CORUMTO, random=~CORUMTO|DYADID/PARTICIP,
> data=new)
> summary(rslint))
>
> at which point I obtain the exact same results for each model suggesting
> that one of the model is not properly specifying the slope or intercept.
>
> Or, I receive the following error message when I try to run the random
> slope/random intercept model.
>
> Error in solve.default(pdMatrix(a, fact = TRUE)) :
> system is computationally singular: reciprocal condition number
> = 6.77073e-017
>
> (whether I receive an error message or the same results depends on the
> specific variables in the model).
>
> It has been suggested that I may need to change the default starting
> values in the model because I may be approaching a boundary-is this a
> plausible explanation for my difficulties? If so, how do I do this in R
> and can you refer me to a source that might highlight what would be
> reasonable starting values?
> If this does not seem like the problem, any idea what the problem may be
> and how I might fix it?
>
> Thank you so much for your assistance,
> Christine Calmes
>
>
> Christine A. Calmes, MA
> Dept of Psychology
> University at Buffalo: The State University of New York
> Park Hall 216
> Buffalo, NY 14260
> ccalmes at buffalo.edu
> (716) 645-3650 x578
>
>
> [[alternative HTML version deleted]]
>
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