1. Harper Adams Utility Poultry Journal Vol. XIV. No. 2 Page 67 Vol. XIV. No. 5 Page 215 Vol. XV. No. 4 Page 175
2. Statistical Methods for Research Workers. R. A. Fisher, 1925.
3. A Study in Sampling Technique. J. Wishart and A. R. Clapham. Journal of Agricultural Science, Vol. XIX, Page 600. 1929.