To cite 'ordinal' in publications use:

Christensen R (2025). ordinal—Regression Models for Ordinal Data. R package version 2025.12-29, https://CRAN.R-project.org/package=ordinal.

Corresponding BibTeX entry:

  @Manual{,
    title = {ordinal---Regression Models for Ordinal Data},
    author = {Rune H. B. Christensen},
    year = {2025},
    note = {R package version 2025.12-29},
    url = {https://CRAN.R-project.org/package=ordinal},
  }