نايف قنيبة نبيل, and خلف حسين حميد. “Estimate Size Sub-Population by Killworth Method”. Journal of Economics and Administrative Sciences 24, no. 108 (November 1, 2018): 439. Accessed May 2, 2025. https://www.jeasiq.uobaghdad.edu.iq/index.php/JEASIQ/article/view/1341.