I have the following model:
> model1<-lmer(aph.remain~sMFS1+sAG1+sSHDI1+sbare+season+crop
+(1|landscape),family=poisson)
…and this is the summary output.
> summary(model1)
Generalized linear mixed model fit by the Laplace approximation
Formula: aph.remain ~ sMFS1 + sAG1 + sSHDI1 + sbare + season + crop
+ (1 | landscape)
AIC BIC logLik deviance
4057 4088 -2019 4039
Random effects:
Groups Name Variance Std.Dev.
landscape (Intercept) 0.74976 0.86588
Number of obs: 239, groups: landscape, 45
Fixed effects:
Estimate Std. Error z value Pr(>|z|)
(Intercept) 2.6613761 0.1344630 19.793 < 2e-16
sMFS1 0.3085978 0.1788322 1.726 0.08441
sAG1 0.0003141 0.1677138 0.002 0.99851
sSHDI1 0.4641420 0.1619018 2.867 0.00415
sbare 0.4133425 0.0297325 13.902 < 2e-16
seasonlate -0.5017022 0.0272817 -18.390 < 2e-16
cropforage 0.7897194 0.0672069 11.751 < 2e-16
cropsoy 0.7661506 0.0491494 15.588 < 2e-16
Correlation of Fixed Effects:
(Intr) sMFS1 sAG1 sSHDI1 sbare sesnlt crpfrg
sMFS1 -0.007
sAG1 0.002 -0.631
sSHDI1 0.000 0.593 -0.405
sbare -0.118 -0.003 0.007 -0.013
seasonlate -0.036 0.006 -0.006 0.003 -0.283
cropforage -0.168 -0.004 0.016 -0.014 0.791 -0.231
cropsoy -0.182 -0.028 0.030 -0.001 0.404 -0.164 0.557
It is probably overdispersed, but how exactly do I calculate this?
Thanks very much.
Best Answer
Among many other useful tidbits on GLMM with lmer() and other GLMM fitting software, check out the section on the following web page called How can I deal with overdispersion in GLMMs?
http://glmm.wikidot.com/faq