To cite npbr in publications use:

Abdelaati Daouia, Thibault Laurent, Hohsuk Noh (2017). npbr: A Package for Nonparametric Boundary Regression in R. Journal of Statistical Software, 79(9), 1-43.<doi:10.18637/jss.v079.i09>

Corresponding BibTeX entry:

  @Article{,
    title = {{npbr}: A Package for Nonparametric Boundary Regression in
      {R}},
    author = {Abdelaati Daouia and Thibault Laurent and Hohsuk Noh},
    journal = {Journal of Statistical Software},
    year = {2017},
    volume = {79},
    number = {9},
    pages = {1--43},
    doi = {10.18637/jss.v079.i09},
  }