[R] Problem specifying Gamma distribution in lme4/glmer
David Winsemius
dwinsemius at comcast.net
Sun Mar 21 22:48:59 CET 2010
On Mar 21, 2010, at 5:16 PM, Ben Bolker wrote:
> Dieter Menne <dieter.menne <at> menne-biomed.de> writes:
>
>> Ben Bolker wrote:
>
>>> 3. zero-inflated data may not be particularly well-represented
>>> by a Gamma distribution: if you actually have a significant number
>>> of exactly-zero values, you may want to analyze your data in two
>>> stages, first as a presence-absence problem and then as a
>>> conditional
>>> density (i.e., what is the distribution of the non-zero values)?
>
>> [...] Do you know of a example where this was done (independent
>> of lmer)? [...]
>
> Nothing springs to mind, but it seems sensible.
I thought this was what hurdle and ZIF models were supposed to handle
gracefully?
--
David.
>
> Ben Bolker
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