[R-sig-ME] Zero variance and Std. Dev. using lmer?

[Renwick, A. R.]

I asked a similar question and got a good reponse last year.
Follow the link below:
https://stat.ethz.ch/pipermail/r-sig-mixed-models/2008q3/001245.html

-----Original Message-----
From: r-sig-mixed-models-bounces at r-project.org [mailto:r-sig-mixed-models-bounces at r-project.org] On Behalf Of Luciano La Sala
Sent: 13 January 2009 14:16
To: r-sig-mixed-models at r-project.org
Subject: [R-sig-ME] Zero variance and Std. Dev. using lmer?

Dear R-people:



I have run a GLMM (using lmer) with the fixed and random effects detailed below. Oddly I think, I get zero variance and Std. Dev. values.

How is that possible? Does it mean that the RE "NestID" is not helping to account for autocorrelation among sibling chicks at the nest level?

Or is this a small sample size problem?



As well, I ran an ordinary logistic regression using he exact same fixed variables, and I got the exact same AIC and BIC values and estimates for fixed effects, error, z value, and Pr(>|z|).



Does this support the idea that the GLMM with RE for NestID is not necessary at all?



Look forward to hearing from you.

Cheers for now.



Luciano





GENERALIZED LINEAR MIXED MODEL WITH RANDOM INTERCEPT



model <- lmer(Death10~HO+ClutchSize+SibComp+Yr+(1|NestID),family=binomial,1)



Generalized linear mixed model fit by the Laplace approximation

Formula: Death10 ~ HO + ClutchSize + Sibcomp + yr + (1 | NestID)



Data: 1

AIC      BIC       logLik     deviance

242.2    268.5     -113.1     226.2



Random effects:

Groups Name           Variance      Std. Dev.

NestID (Intercept)    0                  0



Number of obs: 198, groups: NestID, 104



Fixed effects:

                                   Estimate                     Std. Error
z value             Pr(>|z|)

(Intercept)                   -1.2239                      0.5114
-2.3934           0.0167 *

HOSecond                  -0.6910                      0.8928
-0.7739           0.4390

HOThird                       0.6768                       1.0327
0.6554             0.5122

ClutchSizeTwo-eggs     1.3961                     0.5864             2.3809
0.0173 *

ClutchSizeThree-eggs   0.3958                      0.5843             0.6773
0.4982

SibcompAbsent             1.7804                     0.9140
1.9479             0.0514 .

yr2007                         -0.8299                      0.3423
-2.4245           0.0153 *

---



Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1





Correlation of Fixed Effects:

                          (Intr)      HOScnd     HOThrd     CltchSzTw-
CltchSzTh-   SbcmpA

HOSecond        -0.034

HOThird           -0.031    0.837

CltchSzTw-g   -0.830   -0.069          -0.022

CltchSzThr-      -0.816   -0.088          -0.107         0.785


SibcmpAbsnt     0.052   -0.904          -0.836       -0.018
-0.050

yr2007              -0.233    0.145           0.133         0.025
-0.050       - 0.224






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