[R-sig-ME] Problems withestimationg model in lmer

[Douglas Bates]

2008/2/13 Nicholas Lewin-Koh <lewin-koh.nicholas at gene.com>:
> Consider the attached tumor growth data:
>  dat<-read.table("ListDat.txt",header=TRUE)
>  library(lme4)
>  fit<-lmer(tVol~Dose*poly(Day,2)+(Day|ID),dat)
>  coef(fit)
>  Error in coef(fit) : unable to align random and fixed effects
>  mcmcsamp(fit)
>  Error: no positive eigenvalues!
>  Error in t(.Call(mer_MCMCsamp, object, saveb, n, trans, verbose, deviance))
>  :
>   error in evaluating the argument 'x' in selecting a method for function
>  't'

Could you send us the output of sessionInfo() please?  A call to coef
should not generate .Call(mer_MCMCsamp, ...)

The error message about "unable to align" will go away if you use

tVol ~ Dose*(Day + Day^2) + (Day|ID)

>  detach(package:lme4)
>  library(nlme)
>  fit.lme<-lme(tVol~Dose*poly(Day,2),dat,random=~1+Day|ID)
>  coef(fit.lme)
>  summary(fit.lme)
>
>  works fine in lme. I think this model should be identified, is there an
>  estimation instability I am unaware of? My interest is in prediction not
>  inference, so I am not too concerned about the large number of parameters. I
>  am using the current R-forge version of lme4.
>
>  Thanks
>
>  Nicholas
>  Statistician, Genentech Inc.
>
>
>
>
>   "Seek the company of those who seek the truth, and run away from those who
>  have found it." - Vaclav Havel
>
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