SINGH, H. P.; KARPE, N. On the estimation of ratio and product of two population means using supplementary information in presence. Statistica, [S. l.], v. 69, n. 1, p. 27–47, 2009. DOI: 10.6092/issn.1973-2201/3546. Disponível em: https://rivista-statistica.unibo.it/article/view/3546. Acesso em: 17 may. 2022.