K. Pearson (1900),
On the criterion that a given system of deviations from the probable
in the case of a correlated system of variables is such that it can be
reasonably supposed to have arisen by random sampling,
Philosophical Magazine, 50 (5th series), 157--175.
M. Friendly (2000),
Visualizing Categorical Data.
SAS Institute, Cary, NC.