[R-sig-ME] mixed model?

[Joaquín Aldabe]

Thanks Ben. In this case I considered grass height as continuous. Is it
fine to consider year as random effect with only 4 years?
Best,
Joaquín

2017-05-02 14:49 GMT-03:00 Ben Bolker <bbolker at gmail.com>:

> Minor correction: if GrassHeight is a continuous variable then you
> need (GrassHeight|Field) to model the among-Field variation in the
> effect of grass height.  If GrassHeight is categorical, then
> (GrassHeight|Field) will also work, but it will fit an unstructured
> variance-covariance model (n*(n+1)/2 parameters for an n-level
> categorical predictor), whereas (1|Field/GrassHeight) would fit a
> (positive) compound-symmetric model for the variation in grass height
> effects among fields (2 parameters instead of n*(n+1)/2)
>
> On Tue, May 2, 2017 at 1:36 PM, Joaquín Aldabe <joaquin.aldabe at gmail.com>
> wrote:
> > Thankyou very much Evan. I´ll try that!
> > Cheers,
> > Joaquín.
> >
> > 2017-05-02 14:17 GMT-03:00 Evan Palmer-Young <ecp52 at cornell.edu>:
> >
> >> Joaquin,
> >> It looks like you could use Year and Field as random effects, since
> there
> >> might be variation in bird abundance across years, and similarly,
> variation
> >> across fields.
> >>
> >> So in this case your model is
> >> Birdmodel<- glmer(Presence~ GrassHeight * ForestCover + (1|Year) +
> >> (1|Field), data=BirdData, family =                  "binomial")
> >>
> >> Alternatively you could use Year as a fixed effect, if you are
> interested
> >> in particular years.
> >> Another option is to include interaction terms as random effects, eg
> >> (1|Field:GrassHeight), to allow the effect of GrassHeight to vary across
> >> fields.
> >>
> >>
> >> On Fri, Apr 28, 2017 at 9:32 AM, Joaquín Aldabe <
> joaquin.aldabe at gmail.com>
> >> wrote:
> >>
> >>> Dear all, I'm analysing bird presence/absence in 16 grassland fields
> over
> >>> 4
> >>> seasons (different years) and want to know the effect of grass height
> and
> >>> forest cover on presence/absence of the species. Grass height varied
> among
> >>> season but not forest cover in each field. So we have a spatial
> dimension
> >>> and a time dimension. I tried a binomial glm but wonder if I should use
> >>> generalized linear mixed models with field identity as the random as I
> >>> have
> >>> repeated measures (bird counts) in each field.
> >>>
> >>> I appreciate your opinion.
> >>>
> >>> Thanks in advanced,
> >>>
> >>> Joaquin Aldabe.
> >>>
> >>> --
> >>> *Joaquín Aldabe*
> >>>
> >>> *Grupo Biodiversidad, Ambiente y Sociedad*
> >>> Centro Universitario de la Región Este, Universidad de la República
> >>> Ruta 15 (y Ruta 9), Km 28.500, Departamento de Rocha
> >>>
> >>> *Departamento de Conservación*
> >>> Aves Uruguay
> >>> BirdLife International
> >>> Canelones 1164, Montevideo
> >>>
> >>> https://sites.google.com/site/joaquin.aldabe
> >>> <https://sites.google.com/site/perfilprofesionaljoaquinaldabe>
> >>>
> >>>         [[alternative HTML version deleted]]
> >>>
> >>> _______________________________________________
> >>> R-sig-mixed-models at r-project.org mailing list
> >>> https://stat.ethz.ch/mailman/listinfo/r-sig-mixed-models
> >>
> >>
> >>
> >>
> >> --
> >> Evan Palmer-Young
> >> PhD candidate
> >> Department of Biology
> >> 221 Morrill Science Center
> >> 611 North Pleasant St
> >> Amherst MA 01003
> >> https://scholar.google.com/citations?user=VGvOypoAAAAJ&hl=en
> >> https://sites.google.com/a/cornell.edu/evan-palmer-young/
> >> epalmery at cns.umass.edu
> >> ecp52 at cornell.edu
> >>
> >
> >
> >
> > --
> > *Joaquín Aldabe*
> >
> > *Grupo Biodiversidad, Ambiente y Sociedad*
> > Centro Universitario de la Región Este, Universidad de la República
> > Ruta 15 (y Ruta 9), Km 28.500, Departamento de Rocha
> >
> > *Departamento de Conservación*
> > Aves Uruguay
> > BirdLife International
> > Canelones 1164, Montevideo
> >
> > https://sites.google.com/site/joaquin.aldabe
> > <https://sites.google.com/site/perfilprofesionaljoaquinaldabe>
> >
> >         [[alternative HTML version deleted]]
> >
> > _______________________________________________
> > R-sig-mixed-models at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-sig-mixed-models
>



-- 
*Joaquín Aldabe*

*Grupo Biodiversidad, Ambiente y Sociedad*
Centro Universitario de la Región Este, Universidad de la República
Ruta 15 (y Ruta 9), Km 28.500, Departamento de Rocha

*Departamento de Conservación*
Aves Uruguay
BirdLife International
Canelones 1164, Montevideo

https://sites.google.com/site/joaquin.aldabe
<https://sites.google.com/site/perfilprofesionaljoaquinaldabe>

	[[alternative HTML version deleted]]