@misc{indiciae39f1cfb5050e,
  title = {Modelling the random effects covariance matrix in longitudinal data.},
  author = {Michael J Daniels and Yan D Zhao},
  year = {2003},
  doi = {10.1002/sim.1470},
  url = {https://pubmed.ncbi.nlm.nih.gov/12720301/},
  note = {Source identifier: 12720301}
}