[R-sig-ME] Problem with bootMer and models with offset

[Martin Hecht]

Am 14.10.2014 04:16, schrieb Ben Bolker:
> 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).
the data can be downloaded (for the next 28 days) here:
https://www3.hu-berlin.de/dateiaustausch?g=n2sqg2kpexkgv7n2n9uz
>
>> 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?
the plot looks not that suspicious, except for the strange mean
>
>   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 ...
adding the offset (43.8) manually won't work

thanks for your help!
>
> _______________________________________________
> R-sig-mixed-models at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-sig-mixed-models


-- 
Dipl.-Psych. Martin Hecht

Institut zur Qualitätsentwicklung im Bildungswesen
Humboldt-Universität zu Berlin
Dienstsitz: Luisenstraße 56
Postanschrift: Unter den Linden 6, 10099 Berlin

Tel: +49-(0)30 2093-46589
Fax: +49-(0)30 2093-5336
Email: martin.hecht at iqb.hu-berlin.de
www: http://www.iqb.hu-berlin.de