Getting each bootstrapped data frame from bootMer

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I am trying to get bootstrapped predictions from a logistic glmer
(lme4) object and compare them to the ?observed? independent variable
from each bootstrap iteration. I can use bootMer to get the
bootstrapped predictions:

bb <- bootMer(glmm.M35,
FUN=function(x)predict(x,re.form=NA,newdata=df.fit,type="response"),
nsim=10) # test with just 10 draws

but it doesn?t appear that bootMer saves the replicate datasets. Can
anyone help me modify the bootMer function to output the bootstrap
data frames or at least the independent variable (y) from each? Also
any advice on handling the occasions when an iteration fails to
converge in bootMer would be appreciated.
I would be tempted just to re-invent the guts of bootMer, which are
not actually very complicated -- they're just a simulate/refit loop.  So
I might do something like

nsim <- 10
bootData <- simulate(glmm.M35,nsim)  ## data frame of sim data sets
predvals <- matrix(NA,nrow=length(df.fit),ncol=nsim)
set.seed(101)
for (i  in 1:10) {
   predvals[,i] <- predict(refit(glmm.M35,bootData[[i]]),
                     ...)
}

I also suspect (although haven't tried to check) that bootMer doesn't
use any random numbers other than the ones it uses to generate the
simulations, so you would *probably* be able to retrieve the response
values used if you just did this:

bootMer(...,seed=101)
bootData <- simulate(...,seed=101)

(slightly inefficient, but simulating the data is the smallest part of
the problem)

 hope that helps
    Ben Bolker

}
Thanks, Dan ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Daniel
Hocking Department of Environmental Conservation Northeast Climate
Science Center University of Massachusetts

http://www.danieljhocking.wordpress.com 
dhocking at umass.edu<mailto:dhocking at umass.edu> 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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