Dear R users,

I'm hoping that more experienced users will be able to assist me in
examining the model fit of a mixed generalised linear model. The example
using the data 'bacteria' within the MASS package will hopefully illustrate
what I would like to acheive;

library(MASS)
library(nlme)
attach(bacteria) # y being output and the trt - treatment group being an
explanatory variable. There is pseudoreplication as each patient (ID) is
sampled multiple times (week)

bacteria$y<-1*(bacteria$y=="y")  # to make readable in lmer
table(bacteria$y,bacteria$trt)
hs <- groupedData(y~trt|ID,outer=~trt,data=bacteria)  # I don't think this
is really necessary
model <- lmer(y ~ trt + (week|ID),family=binomial,data=hs)
summary(model)

Here I would like to examine the fit of the variable trt by examining the
residuals. In lm (using lme in "the R book, p. 657"), one would be able to
use

plot(model,trt~resid(.))

However it doesn't work.

If some one would explain why, that would be great. I've come across the
package "zelig", which uses simulation to examine model fit. I haven't
gotten my head round this yet, and was hoping some one would advise the
approp path to take.

Many thanks!

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