Variation ratio
The variation ratio is a simple measure of statistical dispersion in nominal distributions; it is the simplest measure of qualitative variation.
It is defined as the proportion of cases which are not the mode:
where fm is the frequency (number of cases) of the mode, and N is the total number of cases. While a simple measure, it is notable in that some texts and guides suggest or imply that the dispersion of nominal measurements cannot be ascertained. It is defined for instance by (Freeman 1965).