Hi Ben,
Thanks for the quick reply and the useful reference.  My apologies for
hitting the wrong forum; I'll try the others you suggested and see if other
people have anything to add.

- Jason

Date: Thu, 3 May 2012 20:26:51 +0000 (UTC)
From: Ben Bolker <bbolker@gmail.com>
To: r-sig-mixed-models@r-project.org
Subject: Re: [R-sig-ME] Trouble running full ZINB or ZANB model: NaNs
       produced        and errors in optim()
Message-ID: <loom.20120503T222332-275@post.gmane.org>
Content-Type: text/plain; charset=utf-8

J Straka <jstraka@...> writes:

>
> Hello,
>
> I?m attempting to run zero-inflated and hurdle models using the pscl()
> package, but keep encountering problems with running my
> fully-parameterized model and I?m not sure why.
> My data consist of measurements of seed set (the response, which is
> zero-inflated and overdispersed) for two treatments and a control (B,
> F, and O) at three elevations (low, mid, and high).? At each elevation
> I also measured average temperature (AvgTemp) and abundance of insects
> (N).? My goal is to construct a model that best describes seed set
> using the four predictors above (and interactions, if necessary).
> I find that I have no problems running a partial model with only my
> two categorical predictors as follows (just an example using hurdle(),
> but results are the same for zeroinfl()):

 [snip snip]

 This isn't a mixed model question, so it really belongs somewhere
else (r-help or r-sig-ecology spring to mind).

  I wouldn't be shocked if it turned out that your data set was
too small and/or noisy to support what you are trying to do (rule
of thumb is that you probably need about 10 observations per parameter
you are trying to estimate).  I would also suggest centering
(and possibly scaling) your continuous predictors (see
e.g. Schielzeth 2010 Methods in Ecology and Evolution)

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