@article{Clarke2008,
author = {Clarke, P.},
title= {When can group level clustering be ignored? Multilevel models versus single-level models with sparse data},
year = {2008},
doi = {10.1136/jech.2007.060798},
journal = {Journal of Epidemiology and Community Health},
volume = {62},
number = {8},
pages = {752--758},
}