agridat (version 1.8.1)

wedderburn.barley: Percent of barley leaves affected by leaf blotch

Description

Percent of leaf area affected by leaf blotch on 10 varieties of barley at 9 sites.

source

Wedderburn, R W M (1974). Quasilikelihood functions, generalized linear models and the Gauss-Newton method. Biometrika, 61, 439--47.

Details

Incidence of Rhynchosporium secalis (leaf blotch) on the leaves of 10 varieties of barley grown at 9 sites in 1965.

References

McCullagh, P and Nelder, J A (1989). Generalized Linear Models (2nd ed).

Examples

dat <- wedderburn.barley
dat$y <- dat$y/100

dotplot(gen~y|site, dat)

# Use the variance function mu(1-mu).  McCullagh page 330
m1 <- glm(y ~ gen + site, data=dat, family="binomial")
summary(m1)

# Same shape (different scale) as McCullagh fig 9.1a
plot(m1, which=1)

# Compare data and model
dat$pbin <- predict(m1, type="response")
dotplot(gen~pbin+y|site, dat)

# Wedderburn suggested variance function mu^2 * (1-mu)^2
# which is the 'wedderburn' family in the gnm package
library(gnm)
m2 <- glm(y ~ gen + site, data=dat, family="wedderburn")
summary(m2)
# Similar to McCullagh fig 9.2
plot(m2, which=1)

# Compare data and model
dat$pwed <- predict(m2, type="response")
dotplot(gen~pwed+y|site, dat)