The Cholostyramine Data, Table 7.4, p.72

The `cholost.df' data frame has 164 rows and 2 columns.
164 men were supposed to take 6 packets per day of the cholesterol-
lowering drug cholostyramine. Compliance, z, is the percentage of 
the intended dose actually taken. Improvement y is the decrease 
in total plasma cholesterol from the beginning till the end of treatment.

z
compliance, ie. percentage of intended dose actually taken.

y
improvement, ie. the decrease in total plasma cholesterol from 
the beginning till the end of treatment.

Efron, B. & Tibshirani, R.J. (1993)
"An Introduction to the Bootstrap", Chapman & Hall.