Offset() in gls() in nlme

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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