[R] How do I set the dispersion parameter in poisson glm?

[Huso, Manuela]

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?

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