To cite package ‘spdesign’ in publications use:

  Sandorf ED, Campbell D (2023). _spdesign: Designing Stated Preference
  Experiments_. R package version 0.0.5,
  <https://CRAN.R-project.org/package=spdesign>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {{spdesign: Designing Stated Preference Experiments}},
    author = {Erlend Dancke Sandorf and Danny Campbell},
    year = {2023},
    note = {R package version 0.0.5},
    url = {https://CRAN.R-project.org/package=spdesign},
  }