[R-sig-eco] Continuous distribution for zero or positive values (in GLM or GLMM)

[Kyle Hernandez]

You could use the bbmle package http://cran.r-project.org/web/packages/bbmle/index.html

It allows you to use any distribution and very complex models; however, you can't use random effects.  It does require you to program in the distributions, and you will have to use likelihood tests to get a p-value.  But I have had high success with fitting zero-inflated data with this package.
Kyle
On May 18, 2011, at 11:46 AM, Fred Takahashi wrote:

> Hello, just a basic question: what distribution I should use to
> analyze continuous data which can had zero or positive values (eg.
> mass of grasses in plots assuming that zero mass is meaningful)? My
> expected analysis is in the framework of GLM or GLMM (or
> alternatively, GAM / GAMM).
> 
> One idea I had is to add 0.0001 to all values and use family=Gamma.
> That is a good approach?
> 
> If a better choice is to use a different distribution, suggestions of
> packages to do that are welcome.
> 
> Thanks,
> Fred Takahashi
> Universidade de Brasília - Brasil
> 
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Kyle Hernandez
Ph.D. Candidate
Purdue University
Department of Biological Sciences
Lilly B-203
765-494-5894
kmhernan at purdue.edu