@article{Watkins2003,
author = {Watkins, S.C. and Warriner, I.},
title= {How do we know we need to control for selectivity?},
year = {2003},
doi = {10.4054/DemRes.2003.S1.4},
journal = {Demographic Research},
volume = {SC1},
number = {4},
pages = {109--142},
}