housing values in suburbs of Boston.
crim: per capita crime rate by town.
zn: proportion of residential land zoned for lots over 25,000 sq.ft.
indus: proportion of non-retail business acres per town
chas: Charles River dummy variable (= 1 if tract bounds)
nox: nitric oxides concentration (parts per 10 million)
rm: average number of rooms per dwelling
age: proportion of owner-occupied units built prior to 1940
dis: weighted distances to five Boston employment centres
rad: index of accessibility to radial highways
tax: full-value property-tax rate per $10,000
ptratio: pupil-teacher ratio by town
black: 1000(Bk - 0.63)^2 where Bk is the proportion of blacks by town
lstat: percentage of lower status of the population
medv: Median value of owner-occupied homes in $1000's