To cite package ‘birtr’ in publications use:

Kim S (2017). birtr: The R Package for "The Basics of Item Response Theory Using R". R package version 1.0.0, https://CRAN.R-project.org/package=birtr.

Corresponding BibTeX entry:

  @Manual{,
    title = {birtr: The R Package for "The Basics of Item Response
      Theory Using R"},
    author = {Seock-Ho Kim},
    year = {2017},
    note = {R package version 1.0.0},
    url = {https://CRAN.R-project.org/package=birtr},
  }