[R-sig-ME] Offset() in gls() in nlme

[Douglas Bates]

It may work if  you use the offset argument instead of putting an offset
term in the formula.  The model-fitting code in R (and S before it)
sometimes has the "there's more than one way to do it" approach of Perl.
This is convenient for users but not for those writing the code.  I believe
we implemented the offset argument form.

On Wed Nov 12 2014 at 2:52:30 AM ONKELINX, Thierry <Thierry.ONKELINX at inbo.be>
wrote:

> Dear Mark,
>
> In case of a linear model you can create a new variable Y = R - ssb and
> model Y without offset instead of R with ssb as offset. That should give
> the same parameter estimates.
>
> Best regards,
>
> ir. Thierry Onkelinx
> Instituut voor natuur- en bosonderzoek / Research Institute for Nature and
> Forest
> team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
> Kliniekstraat 25
> 1070 Anderlecht
> Belgium
> + 32 2 525 02 51
> + 32 54 43 61 85
> Thierry.Onkelinx at inbo.be
> www.inbo.be
>
> To call in the statistician after the experiment is done may be no more
> than asking him to perform a post-mortem examination: he may be able to say
> what the experiment died of.
> ~ Sir Ronald Aylmer Fisher
>
> The plural of anecdote is not data.
> ~ Roger Brinner
>
> The combination of some data and an aching desire for an answer does not
> ensure that a reasonable answer can be extracted from a given body of data.
> ~ John Tukey
>
> -----Oorspronkelijk bericht-----
> Van: r-sig-mixed-models-bounces at r-project.org [mailto:r-sig-mixed-models-
> bounces at r-project.org] Namens Mark Payne
> Verzonden: dinsdag 11 november 2014 13:23
> Aan: r-sig-mixed-models at r-project.org
> Onderwerp: [R-sig-ME] Offset() in gls() in nlme
>
> Hi,
>
> I am trying to use the following model formula in gls() in the nlme
> package:
>
> R ~ Turb + offset(ssb)
>
> Unfortunately, gls() seems to ignore the offset argument and give results
> that are identical to
>
> R ~ Turb
>
> This is not the case when I use lm() - however, I would like to include a
> corAR1() term as well, which is why I am using gls().
>
> Is this known and intended behaviour? If so, is there a recommended
> workaround/alternative?
>
> Best wishes,
>
> Mark
>
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