To cite package ‘lqmm’ in publications use:

  Geraci M (2014). Linear Quantile Mixed Models: The lqmm Package for
  Laplace Quantile Regression. Journal of Statistical Software, 57(13),
  1-29.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Linear Quantile Mixed Models: The {lqmm} Package for Laplace Quantile Regression},
    author = {Marco Geraci},
    journal = {Journal of Statistical Software},
    year = {2014},
    volume = {57},
    number = {13},
    pages = {1--29},
    doi = {10.18637/jss.v057.i13},
  }

  Geraci M and Bottai M (2014). Linear quantile mixed models.
  Statistics and Computing 24(3), 461-479.

A BibTeX entry for LaTeX users is

  @Article{,
    author = {Marco Geraci and Matteo Bottai},
    title = {Linear quantile mixed models},
    journal = {Statistics and Computing},
    volume = {24},
    number = {3},
    pages = {461--479},
    year = {2014},
    doi = {10.1007/s11222-013-9381-9},
  }

A BibTeX entry for LaTeX users is toBibtex(citation('lqmm'))