Question on random effect
Going back to the independence assumption, see your comment and below my comment (thanks): Joaqu?n 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 ... Joaqu?n 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, Joaqu?n 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, Joaqu?n 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 -- *Joaqu?n Aldabe* *Grupo Biodiversidad, Ambiente y Sociedad* Centro Universitario de la Regi?n Este, Universidad de la Rep?blica Ruta 15 (y Ruta 9), Km 28.500, Departamento de Rocha *Departamento de Conservaci?n* Aves Uruguay BirdLife International Canelones 1164, Montevideo https://sites.google.com/site/joaquin.aldabe <https://sites.google.com/site/perfilprofesionaljoaquinaldabe> <https://www.avast.com/sig-email?utm_medium=email&utm_
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*Joaqu?n Aldabe* *Grupo Biodiversidad, Ambiente y Sociedad* Centro Universitario de la Regi?n Este, Universidad de la Rep?blica Ruta 15 (y Ruta 9), Km 28.500, Departamento de Rocha *Departamento de Conservaci?n* Aves Uruguay BirdLife International Canelones 1164, Montevideo https://sites.google.com/site/joaquin.aldabe <https://sites.google.com/site/perfilprofesionaljoaquinaldabe> [[alternative HTML version deleted]]