# bird species incidence on islands
# Crawley, M.J. (2005) Statistics, An Introduction using R
island <- read.csv(file.choose())
attach(island)
# examine variables
pairs(cbind(incidence,area,isolation,quality,enemy,competitors))
# model with interaction
island.glm1<-glm(incidence~area*isolation, binomial)
island.glm1
summary(island.glm1)
# simpler model
island.glm2<-glm(incidence~area+isolation, binomial)
island.glm2
summary(island.glm2)
# compare models
anova(island.glm1,island.glm2,test="Chi")
# plots
island.glma<-glm(incidence ~ area, binomial)
island.glmi<-glm(incidence ~ isolation, binomial)
par(mfrow=c(1,2))
xv<-seq(0,9,0.01)
yv<-predict(island.glma,list(area=xv),type="response")
plot(area,incidence)
lines(xv,yv)
xv2<-seq(0,10,0.1)
yv2<-predict(island.glmi,list(isolation=xv2),type="response")
plot(isolation,incidence)
lines(xv2,yv2)
par(mfrow=c(1,1))