Expected frequencies, relative risk, odds ratio, and association strength —
mirrors scipy.stats.contingency functions.
expectedFreq computes the expected cell counts under independence from a 2D observed table.
relativeRisk computes the risk ratio and its 95% confidence interval from a 2×2 table.
oddsRatio computes the sample odds ratio and its 95% confidence interval from a 2×2 table.
association measures the strength of association: "phi" for 2×2 tables, "cramer" for larger tables.