د. علي خليفه الشيخ عبد الله; 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, [S. l.], n. 16, p. 81–105, 2020. Disponível em: https://journals.wnu.edu.sd/index.php/wnjsr/article/view/130. Acesso em: 13 jun. 2026.