vcdExtra (version 0.8-5)

Bartlett: Bartlett Data on Plum Root Cuttings

Description

In an experiment to investigate the effect of cutting length (two levels) and planting time (two levels) on the survival of plum root cuttings, 240 cuttings were planted for each of the 2 x 2 combinations of these factors, and their survival was later recorded.

Bartlett (1935) used these data to illustrate a method for testing for no three-way interaction in a contingency table.

Usage

data(Bartlett)

Format

A 3-dimensional array resulting from cross-tabulating 3 variables for 960 observations. The variable names and their levels are:

No	Name	Levels
1	Alive	"Alive", "Dead"
2	Time	"Now", "Spring"
3	Length	"Long", "Short"

References

Bartlett, M. S. (1935). Contingency Table Interactions Journal of the Royal Statistical Society, Supplement, 1935, 2, 248-252.

Examples

data(Bartlett)

# measures of association
assocstats(Bartlett)
oddsratio(Bartlett)

# Test models

## Independence
MASS::loglm(formula = ~Alive + Time + Length, data = Bartlett)

## No three-way association
MASS::loglm(formula = ~(Alive + Time + Length)^2, data = Bartlett)

# Use woolf_test() for a formal test of homogeneity of odds ratios
vcd::woolf_test(Bartlett)


# Plots
fourfold(Bartlett, mfrow=c(1,2))

mosaic(Bartlett, shade=TRUE)
pairs(Bartlett, gp=shading_Friendly)