@inbook{Heckman1982,
author = {Heckman, J.J. and Singer, B.},
title= {The identification problem in econometric models for duration data},
year = {1982},
editor = {Hildenbrand, W.},
booktitle = {Advances in econometrics},
address = {Cambridge},
publisher = {Cambridge University Press},
pages = {39--77},
}