  Covariances from categorical variables are defined using a regular simplex
expression for categories. The method follows the variance definition by Gini,
and it gives the covariance as a solution of simultaneous equations. The
calculated results give reasonable values for test data. A method of principal
component analysis (RS-PCA) is also proposed using regular simplex expressions,
which allows easy interpretation of the principal components. The proposed
methods apply to variable selection problem of categorical data USCensus1990
data. The proposed methods give appropriate criterion for the variable
selection problem of categorical
