Cano, Emilio L., Moguerza, Javier M. and Redchuk, Andres. 2012.
Six Sigma with R. Statistical Engineering for Process
Improvement, Use R!, vol. 36. Springer, New York.
http://www.springer.com/statistics/book/978-1-4614-3651-5.
Gygi C, DeCarlo N, Williams B (2005) Six sigma for dummies. --For dummies,
Wiley Pub.