Problem with bootMer and models with offset

Martin Hecht <martin.hecht at ...> writes:

Hi,

I am using the latest version of R (3.1.1) and lme4 (1.1-7) .

I'm getting some weird implausible bootstrap results from bootMer for a
model with an offset (models without offset work fine).

I've attached an Rdata file with the returned object from lmer (lmerObj)
and the returned object from bootMer (booted)

  Unfortunately, Rdata/RData files get stripped by the mailing list
software (there's a short list of attachments that get allowed --
I'm not sure how to find it -- probably includes txt and CSV files
but not much else).

Any help would be appreciated very much.

the syntax is:

booted <- bootMer ( x = lmerObj , FUN =
function(fit){return(c(fixef(fit),getME(fit,'theta')))} , nsim = 100 ,
seed = 65835 , verbose = TRUE )

booted$t0[1]

(Intercept)
    2.606621

mean(booted$t[,1])

[1] -78.21035

boot::boot.ci ( booted , conf = 0.95 , type = "basic" , index = 1 )

BOOTSTRAP CONFIDENCE INTERVAL CALCULATIONS
Based on 100 bootstrap replicates

CALL :
boot::boot.ci(boot.out = booted, conf = 0.95, type = "basic",
    index = 1)

Intervals :
Level      Basic        
95%   (69.864, 95.425 ) 
Calculations and Intervals on Original Scale
Some basic intervals may be unstable

  This does indeed seem weird.

  Does plot(booted,1) help at all?

  I wonder if a workaround for now is to add the offset manually;
that should be perfectly feasible (if not quite as convenient)
for a linear mixed model -- it's only really *necessary* for
a GLMM ...