To cite betareg in publications use

Achim Zeileis (2009). betareg: Beta Regression. R package version 2.0-0. URL http://CRAN.R-project.org/package=betareg

Corresponding BibTeX entry:

  @Manual{,
    title = {{betareg}: Beta Regression},
    author = {Achim Zeileis},
    year = {2009},
    note = {R package version 2.0-0},
    url = {http://CRAN.R-project.org/package=betareg},
  }