[R-sig-ME] R-structure in ZIP models

[Nicholas Lewin-Koh]

Hi Chris,
If you mean the covariance between the poission parameter and zero
inflation, its because the 
model is not identified. In general though fixing a variance should
expedite MCMC convergence
as 2nd moments require much more information to estimate. But fixing a
parameter tends to
be a pretty strong prior ;)

Nicholas
> 
> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Fri, 08 Jan 2010 12:18:38 -0600
> From: Christopher David Desjardins <desja004 at umn.edu>
> Subject: [R-sig-ME] R-structure in ZIP models
> To: r-sig-mixed-models at r-project.org
> Message-ID: <1262974718.20299.4.camel at debian>
> Content-Type: text/plain; charset="UTF-8"
> 
> I recall that Jarrod recommended that I fix the variance in the
> R-structure when I set priors for ZIP models. However, I don't recall
> why. Was the reason that it expedites MCMC convergence?
> Thanks,
> Chris
> 
> 
> 
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> End of R-sig-mixed-models Digest, Vol 37, Issue 2
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