To cite package 'SixSigma' in publications use:

Emilio L. Cano, Javier M. Moguerza and Andres Redchuk (2012)Six Sigma with R. Springer, New York

Emilio L. Cano, Javier M. Moguerza and Mariano Prieto Corcoba (2015)Quality Control with R. Springer, New York

Corresponding BibTeX entries:

  @Book{,
    title = {Six Sigma with R},
    author = {Emilio L. Cano and Javier M. Moguerza and Andres
      Redchuk},
    year = {2012},
    publisher = {Springer},
    address = {New York},
    volume = {36},
    series = {Use R!},
  }

  @Book{,
    title = {Quality Control with R},
    author = {Emilio L. Cano and Javier M. Moguerza and Mariano Prieto
      Corcoba},
    year = {2015},
    publisher = {Springer},
    address = {New York},
    series = {Use R!},
  }