[R] are hurdle logit-poisson model and posson model nested?

[bbolker]

Wensui Liu wrote:
> 
> Dear Listers,
> I have a general statistical question. Are hurdle logit-poisson model
> and posson model nested?
> 

  You might have to give us a little more detail.  On first glance, my
impression
is that the Poisson model is _not_ nested in the hurdle-Poisson, because the
latter is truncated; what parameter(s) would you set to a fixed value to get
a regular Poisson?  (This is not true, on the other hand, of a zero-inflated
Poisson,
where you could set the zero-inflation parameter to zero to get a Poisson.)
[On the other hand, you would still have a parameter on the boundary of
its feasible space, which would make inference via LRT questionable.)

  good luck
    Ben Bolker

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