1. Albert, A. (1963).— “A Mathematical Theory of Pattern Recognition”. (Ann. Math. Stat., Vol. 34, p. 284).
2. Azorín, F. (1969).— “Curso de muestreo y aplicaciones” (Aguilar, Madrid).
3. Dalenius, Hajek, Zubrcycki (1960).— “On Plane Sampling” (Proc. 4th. Berkeley Symp. on Math. Stat. and Prob. Vol. 1).
4. Das, A. C. (1949).— “Two-Dimensional Systematic Sampling” (Science and Culture, Vol. 15, p. 157, and (1950), Sankhya, Vol. 10, p. 95).
5. Hansen, Hurwitz, Madow (1953).— “Sample Survey Methods and Theory”. (Wiley, N. Y.).