private static double calculateAsymptoticPValue()

in commons-statistics-inference/src/main/java/org/apache/commons/statistics/inference/WilcoxonSignedRankTest.java [501:533]

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

    private static double calculateAsymptoticPValue(double wPlus, int n, double z, double c,
            AlternativeHypothesis alternative, boolean continuityCorrection) {
        // E[W+] = n * (n + 1) / 4 - z * (z + 1) / 4
        final double e = (n * (n + 1.0) - z * (z + 1.0)) * 0.25;

        final double variance = ((n * (n + 1.0) * (2 * n + 1.0)) -
                                (z * (z + 1.0) * (2 * z + 1.0)) - c * 0.5) / 24;

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

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