[R] tweedie and lmer

Ben Bolker bolker at ufl.edu
Thu Aug 27 03:57:12 CEST 2009

Mohammad AlMarzouq <koutbo6 <at> gmail.com> writes:

> Hello all,
> I have count data with about 36% of observations being zeros. I found  
> in some of the examples of the r-help mail archives that a tweedie  
> family of distributions could be used to fit a model with random  
> effects. Upon installing the tweedie package and attempting to fit the  
> following model:
> lmer(SUS ~ 1 + (1| 
> GRP),REML=FALSE,data=mydata,family=tweedie(var.power=1.55,link.power=0))
> I get the following error:
> Error in famType(glmFit$family) : unknown GLM family: ‘Tweedie’
> If it helps, im on a mac with R V 2.9.1, lme4 V.0.999375-31, Tweedie  
> V2.0.

  I'm surprised that you found evidence that tweedie could
be used with lmer: in general, lmer only allows families that
have been hard-coded (and doesn't allow families with "extra"
parameters, such as negative binomial, beta-binomial, tweedie
etc.).  Perhaps you were reading about lme?

  Ben Bolker

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