[R-sig-ME] model comparison in glmmADMB

[RH Gibson, School Biological Sciences]

I am trying to compare two models to see whether the random effect is 
significant, using the anova command I get the following output:

> anova(m7,m8)
Analysis of Variance Table

Model 1: xx ~ nsn * Insect.type + ara * Insect.type + 
offset(logTotal.grains)
Model 2: xx ~ nsn * Insect.type + ara * Insect.type + 
offset(logTotal.grains)
  NoPar  LogLik Df -2logQ P.value
1    12 -2427.4
2    11 -2427.9 -1  -0.96
Warning message:
In pchisq(q, df, lower.tail, log.p) : NaNs produced

Why might this be happening? Can I still use the log likelihood ratio as a 
comparison method? And more generally is this an appropriate test of the 
random effect?

The full models are as follows:

> 
m7<-glmmadmb(x~nsn*Insect.type+ara*Insect.type+offset(logTotal.grains)+(1|Site),data=data1, 
zeroInflation=TRUE, family="nbinom")
>m8<-glmmadmb(x~nsn*Insect.type+ara*Insect.type+offset(logTotal.grains),data=data1, 
zeroInflation=TRUE, family="nbinom")



----------------------
RH Gibson, School Biological Sciences
Rachel.Gibson at bristol.ac.uk