[R-sig-ME] Question on random effect

Thierry Onkelinx thierry.onkelinx at inbo.be
Wed Jul 12 10:02:50 CEST 2017

Dear Joaquin and Ben,

AFAIK have most random effects a term which is i.i.d. The random effects in
nlme and lme4 directly use the i.i.d. term: x_i ~ N(0, \sigma), hence the
random effect itself is i.i.d. INLA has some other constructs available.
e.g. a first order random walk where x_i - x_{i-1} ~ N(0, \sigma). Here the
difference between to consecutive random effects is i.i.d. but the random
effect itself isn't. The available options are listed at
http://www.r-inla.org/models/latent-models

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

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2017-07-11 13:22 GMT+02:00 Ben Bolker <bbolker op gmail.com>:

> Yes, the assumption is that the random effects are (conditionally)
> independent.  It can help to specify covariates  (such as
> latitude/longitude or eastings/northings, or environmental conditions
> [temperature, elevation, etc.]) for sites to mop up some of the
> independence. It is theoretically possible, although I don't know of
> an easy off-the-shelf way to do it, to impose (e.g.) spatial
> correlation structures at the level of the random effects ...  or you
> could examine the spatial dependence of the conditional modes/random
> effects and try to convince yourself it was weak ...
>
> On Tue, Jul 11, 2017 at 7:14 AM, Joaquín Aldabe
> <joaquin.aldabe op gmail.com> wrote:
> > Hi all, when working with mixed models, do the levels of the random
> effect
> > have to be independent? For example, if my random effect is the identity
> of
> > sites and it is associated to the intercept, do sites have to be
> > independent?
> >
> > I appreciate comments and bibliographic references.
> >
> > Thank you very much in advanced,
> >
> > Joaquin
> >
> > --
> > *Joaquín Aldabe*
> >
> > Centro Universitario de la Región Este, Universidad de la República
> > Ruta 15 (y Ruta 9), Km 28.500, Departamento de Rocha
> >
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> > BirdLife International
> > Canelones 1164, Montevideo
> >
> >
> >
> >
> >
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