References/Notes/Attributions:
Source
Michael Friendly (2000), Visualizing Categorical Data, page 18.
References
D. F. Andrews & A. M. Herzberg (1985), Data: A Collection of Problems from Many Fields for the Student and Research Worker. Springer-Verlag, New York, NY.
R. A. Fisher (1925), Statistical Methods for Research Workers. Oliver \& Boyd, London.
L. von Bortkiewicz (1898), Das Gesetz der kleinen Zahlen. Teubner, Leipzig.
M. Friendly (2000), Visualizing Categorical Data. SAS Institute, Cary, NC.