To cite npRmpi in publications use:

  Tristen Hayfield and Jeffrey S. Racine (2008). Nonparametric
  Econometrics: The np Package. Journal of Statistical Software 27(5).
  DOI 10.18637/jss.v027.i05

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Nonparametric Econometrics: The np Package},
    author = {Tristen Hayfield and Jeffrey S. Racine},
    journal = {Journal of Statistical Software},
    year = {2008},
    volume = {27},
    number = {5},
    url = {https://www.jstatsoft.org/index.php/jss/article/view/v027i05},
    doi = {10.18637/jss.v027.i05},
    pages = {1-32},
  }