Nomographs for the Significance of the Difference Between Percentages

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Lawshe, C. H. and Baker, P. C. Three aids in the evaluation of the significance of the difference between percentages. EDUCATIONAL AND PSYCHOLOGICAL MEASUREMENT, 1950, 10, 263-270.

Edwards, A. E. Experimental design in psychological research. (3rd ed.) New York : Holt, Rinehart & Winston, 1968.