Error en mer_finalize(ans) : Downdated X'X is not positive definite, 1. What is wrong with my model?
Dear Ben, Thanks for your response. I had read a very similar response to FAQs explaining why the error relates to rank deficient models. I have tried to center Treatment (a continuous variable, sorry I didn't specify this!) but this does not remove the error. I think the problem comes with the nested nature of "Species" within "Bud_type", since not all species are in all Bud_types, I have a rank deficient design and lme4 cannot cope with it. I do not think there is a solution to this problem other than including "Species" as a random effect, but then I will not be able to know its effect... Cheers, Sara Palacio Quoting Ben Bolker <bbolker at gmail.com>:
PALACIO BLASCO, SARA <s.palacio at ...> writes: [snip]
I am trying to run the following model in glmer:
M_bud_type1=glmer(Dead~Treatment* fBud_type + fBud_type:Species + (1|fRep), family=binomial, data=species)
where: - Dead is a binomial response variable - fBud_type is a fixed factor with 3 levels - Species is a fixed factor with 9 levels nested within fBud_type and - fRep is a random factor with 27 levels nested within Species I have 1386 observations. The error message I receive reads: Error en mer_finalize(ans) : Downdated X'X is not positive definite, 1.
Did you already read the http://glmm.wikidot.com/faq#errors section? It sounds like all your predictors are categorical (although we don't know about Treatment), so centering isn't really as important/as practical an option (you can use sum-to-zero contrasts, but it probably won't make a big difference). Ben Bolker
_______________________________________________ R-sig-mixed-models at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-sig-mixed-models