@article{Horowitz1999,
author = {Horowitz, J.L.},
title= {Semiparametric Estimation of a Proportional Hazard Model with Unobserved Heterogeneity},
year = {1999},
doi = {10.1111/1468-0262.00068},
journal = {Econometrica},
volume = {67},
number = {5},
pages = {1001--1028},
}