Sabtu, S. H. ., M. E. E. M. . Matore, and S. M. . Maat. “Real-World Application: Six Sigma Quality Tools for Continuous Performance Improvement in Specific Educational Practices - A Systematic Review”. International Journal of Learning, Teaching and Educational Research, vol. 22, no. 9, Sept. 2023, pp. 401-22, http://www.ijlter.net/index.php/ijlter/article/view/1749.