[R-sig-ME] PBmodcomp: pwrssUpdate does not converge with glmer

[lorenz.gygax at agroscope.admin.ch]

Dear all,

In a current project (2 x 2 x 2 factorial design) we are interested in
calculating p-values for binary outcomes (we are aware that such an approach
is not unequivocal but circumstances are such that results will most easily
be communicated when we can conduct step-wise backwards model selection and
when we have the p-values).

The experimental design was hierarchically nested (350 observations
conducted in 178 phases of the experiment nested in 90 animal-IDs nested in
24 facilities). The three factors can and should be assigned to three
different hierarchical levels (error, phase, facility).

Even though the data does not look in any way extreme (zeros and ones occur
in all 8 factor combinations), there are some convergence issues with
running the models. These can be mostly dealt with by using: glmerControl
(optimizer= 'bobyqa', optCtrl= list (maxfun= 5000)).

Due to sample size and the assignment of the fixed effects to the different
hierarchical levels, we would like to use parametric bootstrap for
calculating the p-values as implemented in package pbkrtest (very nice!).

Obviously throughout calculating the bootstrap, some of the models will not
converge. As far as I can see, the bootstrap sample is simply accordingly
reduced. Some models, unfortunately, do not result in a warning but in an
error: "pwrssUpdate did not converge in (maxit) iterations with PBmodcomp".

These errors cause PBmodcomp to fail. Does anyone know whether there is a
reason why PBmodcomp reacts differently to warnings and erros in the
bootstrapped glmer's? Or has this just historically grown that the warnings
are captured but the errors are not? If the latter could catching errors be
easily incorporated as well? Where would that need to be done? I cannot find
the according code neither in pbkrtest::PBmodcomp.merMod nor in
pbkrtest::PBrefdist.merMod.

Many thanks for your ideas and best regards, Lorenz
-
Lorenz Gygax, PD Dr. sc. nat.
Federal Food Safety and Veterinary Office FFSVO
Centre for Proper Housing of Ruminants and Pigs