[R] random effects in lmer

From: Line Johansen <line.johansen_at_bio.ntnu.no>
Date: Fri, 22 Aug 2008 14:09:43 +0200

Dear all<>
I am running several generalized mixed model using lmer. <>The models typical look like this:
model2xx<-lmer(numbers~Treatment+b+(1|Genotype)+(1|Field)+(1|Genotype:Treatment), family=quasipoisson)<>
All factors are categorical.

<>And the output looks like this:

Generalized linear mixed model fit using Laplace formula:numbers~Treatment+Dead+(1|Genotype)+(1|Field)+(1|Genotype:Treatment), family=quasipoisson)
Family: quasipoisson(log link)

  AIC BIC logLik deviance

 1033 1051 -509.4 1019

<>Random effects:

Groups Name Variance Std.Dev. Genotype:Treatment (Intercept) 0.40555 0.63683

Genotype                    (Intercept) 1.16642  1.08001
Field                            (Intercept) 1.23738  1.11238
Residual                         9.47740  3.07854
number of obs: 100, groups: Genotype1:Treatment1, 14; Genotype1, 5; Felt1, 4

 Fixed effects:

<>Estimate Std. Error t value

(Intercept)  3.20061    0.80010   4.000
Treatment a -0.05482    0.42619  -0.129
Treatment c  0.08316    0.46395   0.179
Dead No      0.27604    0.14873   1.856

 Correlation of Fixed Effects:<>
(Intr) Tretmnt1 Trtmnt1c

Treatment a -0.247                 
Treatment c -0.239  0.450          
Dead No     -0.111 -0.132    0.003  


I need some help to evaluate the importance of the random factors. The random factor of interest is Genotype. I have tried to delete random factors from the model and comparing the model with the original model by log likelihood-ratio statistics. Is this an appropriate method for testing the random factors in lmer? Is it possible to evaluate how much of the total variation the random factor Genotype explains?  <>
I have am a new user in lmer and my questions is probably very naive. But I appreciate any help.
Thanks for the help. <>


Line Johansen                           

Department of Biology               
Norwegian University of Natural Science and Technology
Høgskoleringen 15
No-7491 Trondheim
Phone: 73 55 12 94

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Received on Fri 22 Aug 2008 - 12:22:00 GMT

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