REFERENCES
- Cochran , W. G. ( 1977 ). Sampling Techniques, 3rd ed. New York : Wiley .
- Scheaffer , R. L. , Mendenhall , W. , Ott , R. L. ( 2006 ). Elementary Survey Sampling, 6th ed. Belmont , CA : Duxbury .
- Williams , B. ( 1978 ). A Sampler on Sampling . New York : Wiley .