@article{Thatcher2002,
author = {Thatcher, R. and Kannisto, V. and Andreev, K.},
title= {The survivor ratio method for estimating numbers at high ages},
year = {2002},
doi = {10.4054/DemRes.2002.6.1},
journal = {Demographic Research},
volume = {6},
pages = {1--18},
}