1. Arul, K., & Kohli, H. (2004). Six-sigma for software application of hypothesis tests to software Data. Software Quality Journal, 12(1), 29–42.
2. Brewer, P., & Bagranoff, N. A. (2004). Near zero-defect accounting with six-sigma. Journal of Corporate Accounting & Finance (Wiley), 15(2), 67–43.
3. Breyfogle, F. W., Cupello, J. M., & Meadows, B. (2001). Managing six-sigma: a practical guide to understanding, assessing, and implementing the strategy that yields bottom-line success. New York, United States: Wiley.
4. Cisco (2019). Cisco Visual Networking Index: Forecast and Trends, 2017–2022 White Paper, Cisco Forecast and Methodology. Retrieved from http://www.cisco.com/en/US/solutions/collateral/ns341/ns525/ns537/ns705/ns827/white_paper_c11-481360_ns827_Networking_Solutions_White_Paper.html
5. Doble, M. (2005). Six-sigma and chemical process safety. International Journal of Six-sigma and Competitive Advantage, 1(2), 229–244.