د. علي خليفه الشيخ عبد الله and د. ياسر تاج السر محمد سند (2020) “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, (16), pp. 81–105. Available at: https://journals.wnu.edu.sd/index.php/wnjsr/article/view/130 (Accessed: 13 June 2026).