@article{Olsen1989,
author = {Olsen, R.J. and Farkas, G.},
title= {Endogenous covariates in duration models and the effect of adolescent childbirth on schooling},
year = {1989},
doi = {10.2307/145932},
journal = {Journal of Human Resources},
volume = {24},
number = {1},
pages = {39--53},
}