@article{Preston1989,
author = {Preston, S.H. and Himes, C. and Eggers, M.},
title= {Demographic conditions responsible for population aging},
year = {1989},
doi = {10.2307/2061266},
URL = {http://dx.doi.org/10.2307/2061266},
volume = {26},
number = {4},
pages = {691--704},
}