To cite package 'cregg' in publications use:

Thomas J. Leeper (2018). cregg: Simple Conjoint Analyses and Visualization. R package version 0.3.0.

Corresponding BibTeX entry:

  @Manual{,
    title = {cregg: Simple Conjoint Analyses and Visualization},
    author = {Thomas J. Leeper},
    year = {2018},
    note = {R package version 0.3.0},
  }