Question on random effect
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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than asking him to perform a post-mortem examination: he may be able to say
what the experiment died of. ~ Sir Ronald Aylmer Fisher
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ensure that a reasonable answer can be extracted from a given body of data.
~ John Tukey
2017-07-11 13:22 GMT+02:00 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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