Contingency coefficient ($C=\sqrt{X^2/(X^2+n)}$)

The contingency coefficient transforms the Pearson chi-squared statistic as $C=\sqrt{X^2/(X^2+n)}$. It is an unsigned measure of statistical association, not a p-value or a direction of an ordinal relationship. Writing ${\varphi }^2=X^2/n$ gives $C=\varphi /\sqrt{1+{\varphi }^2}$. Unlike Cramér's V, its attainable maximum depends on table dimensions, so comparisons between differently sized tables need care.