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

[Ben Bolker]

In that case, I believe Thierry's solution is correct.  For linear models,
offsets are a convenience rather than a necessity.

On Sun, Nov 16, 2014 at 4:40 PM, Mark Payne <mpay at aqua.dtu.dk> wrote:

> Hi Douglas,
>
> Thanks for the reply - unfortunately there doesn't seem to be an offset
> argument either in the latest version of nlme... :-(
>
> > gls
> function (model, data = sys.frame(sys.parent()), correlation = NULL,
>     weights = NULL, subset, method = c("REML", "ML"), na.action = na.fail,
>     control = list(), verbose = FALSE)
>
> > packageDescription("nlme")
> Package: nlme
> Version: 3.1-118
> Date: 2014-10-07
>
> Mark
>
>
> On 13/11/14 04:54, Douglas Bates wrote:
>
>> 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 <mailto: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 <mailto:Thierry.Onkelinx at inbo.be>
>>     www.inbo.be <http://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>
>>     [mailto: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
>>     <mailto: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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>>
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