Displaying 2 results from an estimated 2 matches for "dispersiontest".
2007 Apr 10
1
When to use quasipoisson instead of poisson family
It seems that MASS suggest to judge on the basis of
sum(residuals(mode,type="pearson"))/df.residual(mode). My question: Is
there any rule of thumb of the cutpoiont value?
The paper "On the Use of Corrections for Overdispersion" suggests
overdispersion exists if the deviance is at least twice the number of
degrees of freedom.
Are there any further hints? Thanks.
--
Ronggui
2012 Oct 14
2
Poisson Regression: questions about tests of assumptions
I would like to test in R what regression fits my data best. My dependent
variable is a count, and has a lot of zeros.
And I would need some help to determine what model and family to use
(poisson or quasipoisson, or zero-inflated poisson regression), and how to
test the assumptions.
1) Poisson Regression: as far as I understand, the strong assumption is
that dependent variable mean = variance.