[R-sig-ME] glmer: Downdated X'X is not positive definite

[Ross Boylan]

[Sorry about the recent double-post; you can ignore the second message.]

Ben Bolker wrote
> It is indeed a little surprising (to me) that you're getting 
> downdating problems with an intercept-only model.
>    Hard to say without a closer look at the data.
>    I know it won't solve your problem, but does fitting the model
> _without_ the singleton clusters work?
glmer complained that there were no random terms, as I recall (not at the system now).
glm fit it without complaints.

SAS GLIMMIX fit a poisson with random intercepts to the data without incident.

OTOH, glmer did manage to fit poisson random intercept model to toy
simulated data I constructed, even though the simulated data had lots of
singleton "clusters".

>    Do you have a very small number of values >0?
No.  N > 2,000 and c 1/3 are 1's.

>    I don't see any obvious way to adapt glmer to doing truncated Poisson
> fits, but glmmADMB has a "truncpoiss" family that would be worth trying.
> (Right now glmmADMB is unavailable from r-forge, may be available shortly,
> if you have trouble let me know.)
Thanks for the tip.

My ultimate goal, by the way, is to use the model as part of a chained
equation multiple imputation.  That means it needs to work reliably
without human intervention.

Ross