@article{Heckman1984,
author = {Heckman, J.J. and Singer, B.},
title= {Econometric duration analysis},
year = {1984},
doi = {10.1016/0304-4076(84)90075-7},
journal = {Journal of Econometrics},
volume = {24},
number = {1–2},
pages = {63--132},
}