## ----opts,echo=FALSE----------------------------------------------------------
if (require("knitr")) opts_chunk$set(tidy=FALSE)

## ----dfun---------------------------------------------------------------------
dfun <- function(object) {
  with(object,sum((weights * residuals^2)[weights > 0])/df.residual)
}

## ----dobdata------------------------------------------------------------------
## Dobson (1990) Page 93: Randomized Controlled Trial :
counts <- c(18,17,15,20,10,20,25,13,12)
outcome <- gl(3,1,9)
treatment <- gl(3,3)

## ----fitdob-------------------------------------------------------------------
glmOT.D93 <- glm(counts ~ outcome + treatment, family=poisson)
glmO.D93  <- update(glmOT.D93, . ~ . - treatment)
glmT.D93  <- update(glmOT.D93, . ~ . - outcome)
glmX.D93  <- update(glmT.D93, . ~ . - treatment)
glmQOT.D93 <- update(glmOT.D93, family=quasipoisson)
glmQO.D93 <- update(glmO.D93, family=quasipoisson)
glmQT.D93 <- update(glmT.D93, family=quasipoisson)
glmQX.D93 <- update(glmX.D93, family=quasipoisson)

## ----dobll--------------------------------------------------------------------
(sum(dpois(counts,
          lambda=exp(predict(glmOT.D93)),log=TRUE))) ## by hand
(logLik(glmOT.D93))  ## from Poisson fit

## ----dobll2-------------------------------------------------------------------
(-2*(logLik(glmT.D93)-logLik(glmOT.D93)))  ## Poisson fit
(deviance(glmT.D93)-deviance(glmOT.D93))   ## Poisson fit
(deviance(glmQT.D93)-deviance(glmQOT.D93)) ## quasi-fit

## ----dobdisp------------------------------------------------------------------
(dfun(glmOT.D93))
(sum(residuals(glmOT.D93,"pearson")^2)/glmOT.D93$df.residual)
(summary(glmOT.D93)$dispersion)
(summary(glmQOT.D93)$dispersion)

## ----bbmle--------------------------------------------------------------------
library(bbmle)
(qAIC(glmOT.D93,dispersion=dfun(glmOT.D93)))
(qAICc(glmOT.D93,dispersion=dfun(glmOT.D93),nobs=length(counts)))
ICtab(glmOT.D93,glmT.D93,glmO.D93,glmX.D93,
      dispersion=dfun(glmOT.D93),type="qAIC")
ICtab(glmOT.D93,glmT.D93,glmO.D93,glmX.D93,
      dispersion=dfun(glmOT.D93),
      nobs=length(counts),type="qAICc")
detach("package:bbmle")

## ----AICcmodavg---------------------------------------------------------------
if (require("AICcmodavg")) {
    aictab(list(glmOT.D93,glmT.D93,glmO.D93,glmX.D93), 
           modnames=c("OT","T","O","X"),
           c.hat=dfun(glmOT.D93))
    detach("package:AICcmodavg")
}

## ----MuMin--------------------------------------------------------------------
if (require("MuMIn")) {
    packageVersion("MuMIn")
    ## from ?QAIC
    x.quasipoisson <- function(...) {
        res <- quasipoisson(...)
        res$aic <- poisson(...)$aic
        res
    }
    glmQOT2.D93 <- update(glmOT.D93,family="x.quasipoisson",
                          na.action=na.fail)
    (gg <-  dredge(glmQOT2.D93,rank="QAIC", chat=dfun(glmOT.D93)))
    (ggc <- dredge(glmQOT2.D93,rank="QAICc",chat=dfun(glmOT.D93)))
    detach("package:MuMIn")
}