د. علي خليفه الشيخ عبد الله, and د. ياسر تاج السر محمد سند. “The Effect of Using Six Sigma Methodology Standards in Improving the Performance of the Internal Control System: A Field Study on Government Units in Algezira State”. White Nile Journal for Studies and Research, no. 16 (September 1, 2020): 81–105. Accessed June 13, 2026. https://journals.wnu.edu.sd/index.php/wnjsr/article/view/130.