SINGH, Rajesh; CHAUHAN, Pankaj; SAWAN, Nirmala; SMARANDACHE, Florentin. Improvement in estimating population mean using two auxiliary variables in two-phase sampling. Italian Journal of Pure and Applied Mathematics, [S. l.], v. 28, p. 135–142, 2011. Disponível em: https://journals.uniurb.it/index.php/ijpam/article/view/6001. Acesso em: 18 jul. 2026.