On Thu, 7 Oct 2010, Huso, Manuela wrote:
Dear R users,
I would like to fit a glm with Poisson distribution and log link with a known
dispersion parameter. I do not want to estimate the dispersion parameter. I
know what it is, so I simply want to fix it at a constant for this and other
models to follow. My simple, no covariate model is:
Tall.glm<-glm(Seedling~1,
family=poisson,
offset(log(area)),
data=tallPSME.df)
I want to fix the dispersion parameter at 2.5. How can I do this, please?
The parameter estimation is invariant to the choice of dispersion
parameter, hence you don't have to change anything in the glm() call
above.
Only for the inference you have to set the dispersion, e.g.
summary(Tall.glm, dispersion = 2.5)
hth,
Z
Many thanks in advance for your help,
Manuela
::<>::<>::<>::<>::<>::<>::<>::<>::<
Manuela Huso
Consulting Statistician
201H Richardson Hall
Department of Forest Ecosystems and Society
Oregon State University
Corvallis, OR 97331
ph: 541-737-6232
fx: 541-737-1393
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