[R-sig-ME] Fwd: Could the random effect at the level of each observation be a trap?

Billy billy.requena at gmail.com
Fri Dec 17 22:59:51 CET 2010

```---------- Forwarded message ----------
From: Billy <billy.requena at gmail.com>
Date: Fri, Dec 17, 2010 at 3:57 PM
Subject: Re: [R-sig-ME] Could the random effect at the level of each
observation be a trap?
To: Drew Tyre <atyre2 at unl.edu>

Hi Drew!

Well, below I'm sending the summary of two corresponding models (just
for simplicity, because I have at least 5 models including onlye the
'MaleID' random effect and other 5 including 'MaleID' + 'resid'
randiom effects):

m1 <- glmer (y~ x + (1|MaleID), family=binomial)
m1.1 <- glmer (y~ x + (1|MaleID) + (1|resid), family=binomial)

> summary(m1)
Generalized linear mixed model fit by the Laplace approximation
Formula: y ~ x + (1 | MaleID)
AIC  BIC logLik deviance
1012 1027 -502.9     1006
Random effects:
Groups Name        Variance   Std.Dev.
MaleID (Intercept) 6.9038e-11 8.309e-06
Number of obs: 1045, groups: MaleID, 464

Fixed effects:
Estimate Std. Error z value Pr(>|z|)
(Intercept)   -8.273      2.036  -4.063 4.84e-05 ***
x                   1.192      0.354   3.366 0.000762 ***
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Correlation of Fixed Effects:
(Intr)
x  -0.999

> summary(m1.1)
Generalized linear mixed model fit by the Laplace approximation
Formula: y~ x + (1 | MaleID) + (1 | resid)
AIC   BIC logLik deviance
619.4 639.2 -305.7    611.4
Random effects:
Groups Name        Variance Std.Dev.
resid  (Intercept) 2089.1   45.707
MaleID (Intercept)    0.0    0.000
Number of obs: 1045, groups: resid, 1045; MaleID, 464

Fixed effects:
Estimate Std. Error z value Pr(>|z|)
(Intercept)  -19.049     85.552  -0.223    0.824
x                    1.281     14.844   0.086    0.931

Correlation of Fixed Effects:
(Intr)
x  -0.999

We can see that the variance associated to the 'resid' random variable
is really huge, but I don't really know if that's a problem or it's
just expected due the nature of this individual observation-based
variable.
Furthermore, the correlation between fixed effects seems pretty
strong, but again I don't know if it's a problem.
Does anyone have an insight to help me?

Thanks again

Billy

--
Gustavo Requena
PhD student - Laboratory of Arthropod Behavior and Evolution
Departamento de Ecologia - IBUSP
Rua do Matão - Travessa 14 no 321 Cidade Universitária, São Paulo - SP, Brasil
CEP 05508-900
Phone number: 55 11 3091-7488

http://ecologia.ib.usp.br/opilio/gustavo.html

--
Gustavo Requena
PhD student - Laboratory of Arthropod Behavior and Evolution