To cite package 'GK2011' in publications use:

Thomas J. Leeper (2016). GK2011: Gaines and Kuklinski (2011) Estimators for Hybrid Experiments. R package version 0.1.3.

Corresponding BibTeX entry:

  @Manual{,
    title = {GK2011: Gaines and Kuklinski (2011) Estimators for Hybrid
      Experiments},
    author = {Thomas J. Leeper},
    year = {2016},
    note = {R package version 0.1.3},
  }