[R] system is exactly singular

[rab45+@pitt.edu]

> When trying to fit a generalized linear mixed model using glmmPQL:
>
>> fit0 <- glmmPQL(ifelse(response=="A",1,0)~gender,data=set1,
>     random=~1|subject,family=binomial)
> iteration 1
> Error in solve.default(pdMatrix(a, fact = TRUE)) :
>         Lapack routine dgesv: system is exactly singular
>
> Could this be occuring because the paired responses for each subject are
> always the same? If this were the case, what would be the best way to
> handle this situation?
>
> I replaced the response variable with fake data that are not always the
> same for each pair and then I don't get this (or any) error message.
>
>

Sorry, I forgot that a variable like gender will be the same for both
responses.

Rick B.