@article{bates.etal2015,
  author = {Douglas Bates and Martin Mächler and Ben Bolker and Steve Walker},
  date = {2015},
  doi = {10.18637/jss.v067.i01},
  journaltitle = {Journal of Statistical Software},
  number = {1},
  pages = {1--48},
  title = {Fitting Linear Mixed-Effect Models Using {lme4}},
  volume = {67},
}