[R] question on multilevel modeling

[Christoph Buser]

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 

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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/
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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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