lmer, estimation of p-values and mcmcsamp

(To the list moderator: I just subscribed to the list.  Apologies for not
having done so longer before trying to post.)

Hi all,
     I am currently using lmer to analyze data from an experiment with a
single fixed factor (treatment, 6 levels) and a single random factor
(block). I've been trying to follow the online guidance for estimating
p-values for parameter estimates on these and other help threads:

https://stat.ethz.ch/pipermail/r-help/2006-May/094765.html
http://pidgin.ucsd.edu/pipermail/r-lang/2007-August/000057.html

but have not yet been successful. This is my code:

lnmass <- lmer(log.mass ~ treatment + (1|block), data=exp1)
summary(lnmass)

samp <- rnorm(n=10000)
mcmcpvalue <- function(samp)
     {std <- backsolve(chol(var(samp)),
          cbind(0,t(samp)) - colMeans(samp),
          transpose = TRUE)
     sqdist <- colSums(std*std)
     sum(sqdist[-1] > sqdist[1]/nrow(samp) }

markov1 <- mcmcsamp(lnmass, 10000)
HPDinterval(markov1)

mcmcpvalue(as.matrix(markov1[,1]))
mcmcpvalue(as.matrix(markov1[,2]))
mcmcpvalue(as.matrix(markov1[,3]))
mcmcpvalue(as.matrix(markov1[,4]))
mcmcpvalue(as.matrix(markov1[,5]))
mcmcpvalue(as.matrix(markov1[,6]))

The first time I tried it HPDinterval generated CIs for each treatment
level, etc. but after each of the last 6 lines of code I received the
following error messages:

Error in markov[,1] : object is not subsettable
Error in as.matrix(markov1[,1]) : error in evaluating the argument 'x' in
selecting a method for function  'as.matrix'
Error in chol(val(samp)) : error in evaluating the argument 'x' in
selecting
a method for function 'chol'

When I came back to it today HPDinterval(markov1) also no longer worked
and
gave me the following error message:

Error in UseMethod("HPDinterval"): no applicable method for "HPDinterval"

I imagine at least some of this has to do with the fact that I don't fully
understand what exactly the mcmcpvalue function is doing.  Any help on
either problem would be very much appreciated.

Thanks, Maureen

*****
Maureen Ryan
Department of Evolution and Ecology
University of California Davis
One Shields Avenue
Davis, CA 95616
(530)304-2266

	[[alternative HTML version deleted]]