[R] Example of mcmcsamp() failing with lmer() output

Michael Kubovy kubovy at virginia.edu
Fri Apr 27 18:58:30 CEST 2007


I would appreciate help with the following model

gunload <- read.table(hh('datasets/gunload.dat'), header = T)
gunload$method <- factor(gunload$method, labels = c('new', 'old'))
gunload$physique <- factor(gunload$group, labels = c('slight',  
'average', 'heavy'))
gunload$team9 <- factor(rep(1:9, each = 2))

This is a split plot design with randomly selected teams for each  
physique, which was crossed with two methods.

Following the Oats example in chap. 1 of MEMSS, and adapting to lmer:

gl.lmer <- lmer(rounds ~ method * physique + (1 | physique/team),  
data = gunload)
lmer runs as expected, but mcmcsamp() gives:
Error: Leading minor of order 1 in downdated X'X is not positive  
Error in t(.Call(mer_MCMCsamp, object, saveb, n, trans, verbose,  
deviance)) :
	error in evaluating the argument 'x' in selecting a method for  
function 't'

I tried:

gl.lme <- lme(rounds ~ method * physique, random = ~1 | physique/ 
team, data = gunload)
which gave all the expected output except that two p-values were NaN.

Which aspect of the data is making the simulation fail, and is there  
anything to be done about it?

Professor Michael Kubovy
University of Virginia
Department of Psychology
USPS:     P.O.Box 400400    Charlottesville, VA 22904-4400
Parcels:    Room 102        Gilmer Hall
         McCormick Road    Charlottesville, VA 22903
Office:    B011    +1-434-982-4729
Lab:        B019    +1-434-982-4751
Fax:        +1-434-982-4766
WWW:    http://www.people.virginia.edu/~mk9y/

More information about the R-help mailing list