@article{Watkins2003,
author = {Watkins, S. 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 Special Collection},
volume = {1},
number = {4},
pages = {109--142},
}