vcdExtra (version 0.5-3)

Alligator: Alligator Food Choice

Description

The Alligator data, from Agresti (2002), comes from a study of the primary food choices of alligators in four Florida lakes. Researchers classified the stomach contents of 219 captured alligators into five categories: Fish (the most common primary food choice), Invertebrate (snails, insects, crayfish, etc.), Reptile (turtles, alligators), Bird, and Other (amphibians, plants, household pets, stones, and other debris).

Usage

data(Alligator)

source

Agresti, A. (2002). Categorical Data Analysis, New York: Wiley, 2nd Ed., Table 7.1

Details

The table contains a fair number of 0 counts. food is the response variable. fish is the most frequent choice, and often taken as a baseline category in multinomial response models.

Examples

data(Alligator)

# change from frequency data.frame to table
allitable <- xtabs(count~lake+sex+size+food, data=Alligator)
# Agresti's Table 7.1
structable(food~lake+sex+size, allitable)


plot(allitable, shade=TRUE)
# mutual independence model
mosaic(~food+lake+size, allitable, shade=TRUE)
# food jointly independent of lake and size
mosaic(~food+lake+size, allitable, shade=TRUE, expected=~lake:size+food)

if (require(nnet)) {
	# multinomial logit model
	mod1 <- multinom(food ~ lake+size+sex, data=Alligator, weights=count)
}