## Data set from Agresti, 2007.

# Data: Study of nesting horseshoe crabs (J. Brockman, Ethology, 1996).
# Each female crab in the study had a male crab attached to her in her nest.
# The study investigated factors that affect whether the female crab had
# any other males, called satellites, residing nearby her.
# Explanatory variables thought possibly to affect this included the
# female crab's color, spine condition, weight, and carapace width.
# The response outcome for each female crab is her number of satellites.
# We will look at the response has a binary random variable:
# 0 = no satellites, 1 = at least one satellite

# Variable descriptions:
# color: 1 - light medium, 2 - medium, 3 - dark medium, 4 - dark
# spine: 1 - both good, 2 - one worn or broken, 3 - both worn or broken
# width: carapace width in cm
# satell: number of satellites
# weight: weight in kg

crab <- read.table("http://www.math.montana.edu/shancock/courses/stat539/data/horseshoe.txt",header=T)

# Consider both binary and count responses:
crab$sat.ind <- as.numeric(crab$satell > 0)