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, Sept. 2020, pp. 81-105, doi:10.67135/wnj.2020.1604.