@article{waterman2015several,
  author = {Megan J. Waterman and Jeffrey B. Birch and Abdel-Salam G. Abdel-Salam},
  title = {Several nonparametric and semiparametric approaches to linear mixed model regression},
  year = {2015},
  journal = {Journal of Statistical Computation and Simulation},
  volume = {85},
  number = {5},
  pages = {956--977},
  publisher = {Informa UK Limited},
  doi = {10.1080/00949655.2013.856435}
}