To cite package 'RSA' in publications use:

Schönbrodt, F. D. & Humberg, S. (2018). RSA: An R package for response surface analysis (version 0.9.13). Retrieved from https://cran.r-project.org/package=RSA

Corresponding BibTeX entry:

  @Manual{,
    title = {{RSA}: An R package for response surface analysis (version
      0.9.13)},
    author = {Felix D. Schönbrodt and Sarah Humberg},
    year = {2018},
    url = {https://cran.r-project.org/package=RSA},
  }