Cheosuwan, T., S. Saipanya, and S. Tongphet. “The Improvement of a Quality Assurance Information Systems Based Six-Sigma Principles”. ECTI Transactions on Computer and Information Technology (ECTI-CIT), vol. 11, no. 1, Apr. 2017, pp. 20-27, doi:10.37936/ecti-cit.2017111.66571.