[R] R-help Digest, Vol 171, Issue 20

David Winsemius dwinsemius at comcast.net
Mon May 29 21:42:30 CEST 2017

> On May 28, 2017, at 11:53 PM, Brigitte Mangin <brigitte.mangin at inra.fr> wrote:
> Thanks Ron,
> In fact, I want to make a model choice using different fixed structures and using the results of:
> Gurka MJ (2006) Selecting the best linear mixed model under reml. The American Statistician 60(1):19{26,
> the best criterium uses the reml likelihood.
> I asked the ASREML-r developpers and they answered that their results were checked against GENSTAT.
> I think it is not really a good think for the R community to compute a REML likelihood that is probably not the REML likelihood.

Is it your understanding that REML values should be different somehow than other likelihoods with respect to the fact that you should only be comparing _differences_ in model likelihoods calculated on the same data? The value of a likelihood is only specified up to a constant (as Thierry Onkelinx already pointed out.)

I can get different deviances (-2*log(likelihood) in glm poisson models by just grouping data elements and modeling counts. But varying models will have the same differences in deviance regardless of grouping or not.

Looking at this copy of that citation It appears to me that differences (comparing full to reduced) in various criteria for models is what is under discussion:


You should show some results rather than letting this discussion remain so vague.


> Brigitte
> Brigitte Mangin, INRA, LIPM, CS 52627, 31326 CASTANET-TOLOSAN
> tel: 33 + (0)5 61 28 54 58
> ________________________________________
> De : Crump, Ron <R.E.Crump at warwick.ac.uk>
> Envoyé : mardi 23 mai 2017 10:29
> À : r-help at r-project.org; Brigitte Mangin
> Objet : Re: R-help Digest, Vol 171, Issue 20
> Hi Brigitte,
>> Did somebody know why asreml does not provide the same REML loglikehood
>> as coxme, lme4 or lmne.
> I don't know the answer to this, but I'd guess it is either to do with the
> use of the average information REML algorithm or asreml-r is for some
> reason ending up with a different subset of the data.
>> If it was just a constant value between the two models (with or without
>> the fixed effect) it would not be important. But it is not.
>> I checked that the variance component estimators were equal.
> I'm still not clear that it is important (if the data subset analysed is
> the same). You would only use the REML likelihoods to compare models with
> different random effects and the same fixed effect structure (is there
> another use for the REML likelihood other than that?), so then it is
> really a question of whether for a given pair of random effect models and
> the same data the likelihood ratio test statistic  changes across analysis
> methods. Unless for some reason you are comparing two random effect models
> fitted with different routines (one of which is asreml-r).
> Ron.
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David Winsemius
Alameda, CA, USA

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