[R-sig-ME] Question on random effect

[Joaquín Aldabe]

Going back to the independence assumption, see your comment and below my
comment (thanks):

Joaquín asked: 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?

Ben said:
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 ...

Joaquín current comment: However, I´ve seen that response observations
inside a random effect variable may be correlated, and this can be
quantified by Intraclass Correlation Coefficients (ICCs). Is this lack of
independence among random effect levels?

On Tue, Jul 11, 2017 at 7:14 AM, Joaquín Aldabe
<joaquin.aldabe at gmail.com> wrote:

2017-07-11 8:22 GMT-03:00 Ben Bolker <bbolker at 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 at 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*
> >
> > *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>
> >
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-- 
*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>

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