Bartkus, Ignas, and Aleksandras Plikusas. “The Generalization of Ratio-Cum Product Estimator for the Arbitrary Sample Design”. Lietuvos matematikos rinkinys 50, no. proc. LMS (December 20, 2009): 275–280. Accessed May 4, 2024. https://www.journals.vu.lt/LMR/article/view/17977.