@article{RRACEFN_1999_1999_1_a7,
     author = {HousiLA P. SINGH AND M. RUIZ ESPEJO},
     title = {A class of {PPS} estimators variance using auxihary information.},
     journal = {Revista de la Real Academia de Ciencias Exactas, F{\'\i}sicas y Naturales},
     pages = {217-220},
     year = {1999},
     volume = {93},
     number = {2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RRACEFN_1999_1999_1_a7/}
}