@article{Kallan1986,
author = {Kallan, J. and Udry, J.R.},
title= {The determinants of effective fecundity based on the first birth interval},
year = {1986},
doi = {10.2307/2061407},
journal = {Demography },
volume = {23},
number = {1},
pages = {53--66},
}