private double calculateAsymptoticPValue()

in commons-statistics-inference/src/main/java/org/apache/commons/statistics/inference/MannWhitneyUTest.java [344:377]

• 25 lines of code
• 6 McCabe index (conditional complexity)

    private double calculateAsymptoticPValue(double u, int n1, int n2, double c) {
        // Use long to avoid overflow
        final long n1n2 = (long) n1 * n2;
        final long n = (long) n1 + n2;

        // https://en.wikipedia.org/wiki/Mann%E2%80%93Whitney_U_test#Normal_approximation_and_tie_correction
        final double e = n1n2 * 0.5;
        final double variance = (n1n2 / 12.0) * ((n + 1.0) - c / n / (n - 1));

        double z = u - e;
        if (continuityCorrection) {
            // +/- 0.5 is a continuity correction towards the expected.
            if (alternative == AlternativeHypothesis.GREATER_THAN) {
                z -= 0.5;
            } else if (alternative == AlternativeHypothesis.LESS_THAN) {
                z += 0.5;
            } else {
                // two-sided. Shift towards the expected of zero.
                // Use of signum ignores x==0 (i.e. not copySign(0.5, z))
                z -= Math.signum(z) * 0.5;
            }
        }
        z /= Math.sqrt(variance);

        final NormalDistribution standardNormal = NormalDistribution.of(0, 1);
        if (alternative == AlternativeHypothesis.GREATER_THAN) {
            return standardNormal.survivalProbability(z);
        }
        if (alternative == AlternativeHypothesis.LESS_THAN) {
            return standardNormal.cumulativeProbability(z);
        }
        // two-sided
        return 2 * standardNormal.survivalProbability(Math.abs(z));
    }