The censored regression model was first introduced into economics by Tobin (1958)
in his pioneering study of household expenditure on durable goods where he explicitly
allowed for the fact that the dependent variable, namely the expenditure on durables,
cannot be negative. The model suggested by Tobin and its various generalizations are
known in economics as Tobit models and are surveyed in detail by Amemiya (1984), and
more recently in Cameron and Trivedi (2005, ch. 14).