[R-sig-eco] Negative binomial

[Stratford, Jeffrey]

Oi Joao,

>From my understanding of the Poisson, as the Poisson mean (lambda) increases, the distribution converges with the mean.  I believe there are also issues with the intercept since counts cannot be negative.  If the variance is excessive (var/df >> 1) then switch to negative binomial. So go ahead with the Poisson first then check results.   

This is my first post with my stats cap on.. and I'll let others decide if I'm right (I'll do a little dance if I am).

HTH,

Jeff

 
********************************************
Dr. Jeffrey A. Stratford
Assistant Professor of Biology 
Department of Biology and Health Sciences
WIlkes University, PA 18766
570-332-2942 (cell and preferred)
570-408-4761 (office) 
http://web.wilkes.edu/jeffrey.stratford/
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-----Original Message-----
From: r-sig-ecology-bounces at r-project.org [mailto:r-sig-ecology-bounces at r-project.org] On Behalf Of Canning-Clode, Joao
Sent: Thursday, October 01, 2009 2:30 PM
To: r-sig-ecology at r-project.org
Subject: [R-sig-eco] Negative binomial

Hi all,

1st time user here!
I am an ecologist working with marine fouling assemblages. I just got a paper back for revision. I am working with count data (species richness). I have used a linear model but the reviewers are recommending the use of negative binomial or Poisson. As far as I could understand from the literature these complex models should be used and the distribution is skewed left (lots of zeros). Well, my data is perfectly normal distributed. My main question is: can I still use negative binomial or poisson even if my data is normal? Does that make sense?

Thanks in advance

João Canning Clode, PhD
Postdoctoral Fellow
Marine Invasions Research Lab
Smithsonian Environmental Research Center
647 Contees Wharf Road
Edgewater, MD 21037

Email: canning-clodej at si.edu
Web: www.canning-clode.com
Tel: 443-482-2354

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