To cite package 'SixSigma' in publications use:

Emilio L. Cano, Andres Redchuk, Javier M.Moguerza, (2-02). SixSigma: Six Sigma Tools for Quality and Process Improvement R package version 0.6.0.

Corresponding BibTeX entry:

  @Manual{,
    title = {SixSigma: Six Sigma Tools for Quality Improvement},
    author = {Emilio L. Cano and Javier M. Moguerza and Andres
      Redchuk},
    year = {2-02},
    note = {R package version 0.6.0},
  }