@article{Christensen2009,
author = {Christensen, Kaare and Doblhammer, Gabriele and Rau, Roland and Vaupel, James W},
title= {Ageing populations: the challenges ahead },
year = {2009},
doi = {10.1016/S0140-6736(09)61460-4},
journal = {The Lancet},
volume = {374},
number = {9696},
pages = {1196 -- 1208},
}