@article{Heckathorn2007,
author = {Heckathorn, D.},
title= {Extensions of respondent-driven sampling: Analyzing continuous variables and controlling for differential recruitment},
year = {2007},
doi = {10.1111/j.1467-9531.2007.00188.x},
volume = {37},
number = {1},
pages = {151--208},
}