To cite package ‘twins’ in publications use:

  Held L, Hofmann M, Höhle M, Schmid V (2006). “A two-component model
  for counts of infectious diseases.” _Biostatistics_, *7*(3), 422-437.
  doi:10.1093/biostatistics/kxj016
  <https://doi.org/10.1093/biostatistics/kxj016>.

A BibTeX entry for LaTeX users is

  @Article{,
    author = {Leonhard Held and Mathias Hofmann and Michael Höhle and Volker Schmid},
    title = {A two-component model for counts of infectious diseases},
    journal = {Biostatistics},
    volume = {7},
    number = {3},
    pages = {422--437},
    year = {2006},
    doi = {10.1093/biostatistics/kxj016},
  }