@article{Liang1986,
author = {Liang, K.Y. and Zeger, S.L.},
title= {Longitudinal data analysis using generalized linear models},
year = {1986},
doi = {10.1093/biomet/73.1.13},
journal = {Biometrika},
volume = {73},
number = {1},
pages = {13--22},
}