1. "A.S.T.M. Manual on Presentation of Data," Philadelphia , American Society for Testing Materials, April, 1943, p. 1.
2. Worthing, A.G., and Geffner, J. "Treatment of Experimental Data," New York, John Wiley and Sons, 1943, pp. 177 ff.
3. Davies, G.R., and Crowder, W.F. "Methods of Statistical Analysis in the Social Sciences," New York, John Wiley and Sons, 1933 , p. 303.