1. 1. D. J. Finney : Experimental Design and Its Statistical Basis . Chicago, University of Chicago Press, 1955 , pp.3 , 3 , 3 , 3 , 3 .
2. 4. A. B. Hill : Principles of Medical Statistics . 8th edition . New York, Oxford University Press, 1967 , pp.251 , 251 -357 .
3. 5. J. L. Fleiss : Statistical Methods for Rates and Proportions . New York, John Wiley & Sons, 1973 , pp.35 -38 .