@article{liang1986,
  title={Longitudinal data analysis using generalized linear models},
  author={Kung‐Yee Liang and Scott L. Zeger},
  year={1986},
  journal={Biometrika},
  doi={10.1093/biomet/73.1.13},
  url={https://doi.org/10.1093/biomet/73.1.13}
}