[R-sig-ME] glmmTMB predicted values and AIC, vs glmer

[John Maindonald]

The code that follows below demonstrates what I find a very odd
issue with r-sig-mixed-models using r-project.org<mailto:r-sig-mixed-models using r-project.org>, and with the comparison between
glmmTMB::glmmTMB and lme4::glmer, for models that have the
same model formulae.

1) In the glmmTMB model as fitted to `ffly`, one predicted value is
infinite.  This, even though all coefficients and standard errors
have finite values.  This surely indicates that there is something
odd in the way that predictions on the scale of the linear
predictor are calculated.

2) Initially, I'd thought that the `Inf` value explained the
difference between the two AIC values.  But the difference
pretty much stays the same when the "offending" point is
removed.

I've not checked what happens when there are no observation level
random effects.  Is there some difference in the way that the
model formulae are interpreted in the two cases?


ffly <- read.csv('https://github.com/jhmaindonald/dataR/files/6521483/ffly.csv')
ffly$obs <- factor(ffly$obs)

form1 <- cbind(Dead,Live)~0+trtGp/TrtTime+(1|obs)+(1|trtGpRep)

library(lme4); library(glmmTMB)
ObsTMB.cll <- glmmTMB(form1,
                      family=binomial(link="cloglog"), data=ffly)
Obsglmer.cll <- glmer(form1, nAGQ=0,
                      family=binomial(link="cloglog"), data=ffly)

round(AIC(Obsglmer.cll, ObsTMB.cll), 2)
##                      df    AIC
## Obsglmer.cll 14 639.44
## ObsTMB.cll  14 636.02

round(c(max(predict(ObsTMB.cll)),max(predict(Obsglmer.cll))),3)
## [1]   Inf 3.833

range(fixef(ObsTMB.cll))
## [1] -5.28780064553  1.15952249272
range(vcov(ObsTMB.cll))
## [1] -0.0546986905338  0.2887049942215

## Try also; there are small deviations from the line
plot(predict(Obsglmer.cll)~predict(ObsTMB.cll))
abline(0,1)

## Remove offending point
ffly1 <- ffly[-which.max(predict(ObsTMB.cll)),]
ObsTMB1.cll <- glmmTMB(form1,
                      family=binomial(link="cloglog"), data=ffly1)
Obsglmer1.cll <- glmer(form1, nAGQ=0,
                      family=binomial(link="cloglog"), data=ffly1)

cbind(AIC(Obsglmer.cll, ObsTMB.cll), AIC1=AIC(Obsglmer1.cll, ObsTMB1.cll)[,2])
##                       df                    AIC                  AIC1
## Obsglmer.cll  14 639.441888969 639.441889196
## ObsTMB.cll   14 636.016597730 636.016597723
  ## Observe that changes are in the final four decimal places.


round(rbind(glmer=fixef(Obsglmer1.cll),
TMB=unclass(fixef(ObsTMB1.cll)$cond)),3)

      trtGpspAEgg trtGpspAL2 trtGpspAL3 trtGpspBEgg trtGpspBL2 trtGpspBL3
glmer       0.772     -2.255     -3.299      -1.803     -2.632     -5.114
TMB         0.790     -2.367     -3.441      -1.889     -2.757     -5.288
      trtGpspAEgg:TrtTime trtGpspAL2:TrtTime trtGpspAL3:TrtTime
glmer               0.231              0.372              0.563
TMB                 0.288              0.398              0.602
      trtGpspBEgg:TrtTime trtGpspBL2:TrtTime trtGpspBL3:TrtTime
glmer               0.278              0.517              1.112
TMB                 0.299              0.554              1.160


John Maindonald             email: john.maindonald using anu.edu.au<mailto:john.maindonald using anu.edu.au>


	[[alternative HTML version deleted]]