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 river; 0 otherwise)) 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) B (1000(Bk - 0.63)^2 where Bk is the proportion of black people by town) LSTAT (% lower status of the population)