@article{Li2005,
author = {Li, N. and Lee, R.},
title= {Coherent mortality forecasts for a group of populations: An extension of the lee-carter method},
year = {2005},
doi = {10.1353/dem.2005.0021},
journal = {Demography},
volume = {42},
number = {3},
pages = {575--594},
}