@article{MET_1972__18_175509,
     author = {T.J. Rao},
     title = {On the {Variance} of the {Ratio} {Estimator.}},
     journal = {Metrika},
     pages = {209--215},
     publisher = {mathdoc},
     volume = {18},
     year = {1972},
     zbl = {0242.62017},
     url = {http://geodesic.mathdoc.fr/item/MET_1972__18_175509/}
}