@article{Abbring2007,
author = {Abbring, J. H. and van den Berg, G. J.},
title= {The Unobserved Heterogeneity Distribution in Duration Analysis},
year = {2007},
doi = {10.1093/biomet/asm013},
journal = {Biometrika},
volume = {94},
number = {1},
pages = {87--99},
}