1. G. W. Snedecor and W. G. Cochran, “Statistical Methods,” 6th Edition, Iowa State Univ. Press, Ames, Iowa, 1967, Chapter 4.
2. J. E. Nelson, “Vitamin E: A Comprehensive Treatise,” ed. by L. J. Machlin, Marcel Dekker Inc., New York and Basel, 1980, p. 397.