[R] Problem specifying Gamma distribution in lme4/glmer

Matthew Giovanni matthewgiovanni at gmail.com
Sat Mar 20 23:54:42 CET 2010

Dear R and lme4 users-

I am trying to fit a mixed-effects model, with the glmer function in
lme4, to right-skewed, zero-inflated, non-normal data representing
understory grass and forb biomass (continuous) as a function of tree
density (indicated by leaf-area).  Thus, I have tried to specify a
Gamma distribution with a log-link function but consistently receive
an error as follows:

> total=glmer(total~gla4+(1|plot)+(1|year/month),data=veg,family=Gamma(link=log))
> summary(total)
Error in asMethod(object) : matrix is not symmetric [1,2]

I have also tried fitting glmm's with lme4 and glmer to other
Gamma-distributed data but receive the same error.  Has anyone had
similar problems and found any solutions?

Thank you for your input.  Best regards,
Matt Giovanni, Ph.D.
NSERC Visiting Research Fellow
Canadian Wildlife Service
2365 Albert St., Room 300
Regina, SK S4P 4K1
306-780-6121 work
402-617-3764 mobile

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