The Common Structure of Statistical Models of Truncation, Sample Selection and Limited Dependent Variables and a Simple Estimator for Such Models

James J. Heckman, Annals of Economic and Social Measurement, Volume 5, number 4 (NBER, 1976), chap. 6, https://www.nber.org/books-and-chapters/annals-economic-and-social-measurement-volume-5-number-4/common-structure-statistical-models-truncation-sample-selection-and-limited-dependent-variables-and.