---------- Forwarded message ----------
From: alexander russell <ssv736@gmail.com>
Date: Tue, Oct 20, 2009 at 4:34 PM
Subject: Re: [R] When modeling with negbin from the aod package...
To: Matthieu Lesnoff <matthieu.lesnoff@gmail.com>


Hello again,

It seems that, though we have a simple estimate of the variance, phi, with
negbin, some models seek to create a formula for the variance.

For example, I think Bolker has modeled  variance in the Lily_sum data set
as

*nlikfun = function(a, c, d) {*

*+ k = c * exp(d * flowers)*

*+ -sum(dnbinom(seedlings, mu = a, size = k, log = TRUE))*

*+ }*

(book, p. 420)

if I'm correct?
Is it fair to say that the 'random' argument for negbin will model variance
this way only if the independent variable on which the variance depends in
the "right-hand formula" is categorical or is a factor with a few levels
only?
regards, s
  On Thu, Oct 15, 2009 at 5:53 PM, Matthieu Lesnoff <
matthieu.lesnoff@gmail.com> wrote:

> >that is they are
> > maximum likelihood estimates. Would someone tell me if I'm correct?
>
> yes, all parameters estimated with negbin (aod) are ML estimates
>
> Regards
>
> Matthieu
>
>

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