@article{Stover2000,
author = {Stover, J. and Bertrand, J.T. and Shelton, J.D.},
title= {Empirically based conversion factors for calculating couple-years of protection},
year = {2000},
doi = {10.1177/0193841X0002400101},
volume = {23},
number = {1},
pages = {3--46},
}