n=40
##generate data
X=rnorm(n, mean=0.5, sd=1)
lam=exp(0.2+0.5*X)
Y=rpois(n,lam)
plot(Y~X)

##fit model
fit.p=glm(Y~X, family="poisson")
summary(fit.p)

##Deviance test
with(fit.p, cbind(res.deviance = deviance, df = df.residual,
  p = pchisq(deviance, df.residual, lower.tail=FALSE)))

##improvement test
fit.p0=update(fit.p, .~.-X)
anova(fit.p0, fit.p, test="Chisq")

##NB model
Y=rnbinom(n, mu=lam, size=2)
library(MASS)
fit.nb=glm.nb(Y~X)
fit.nb
summary(fit.nb)

##odTest
library(pscl)
odTest(fit.nb)