MathPHP\Statistics\Significance::chiSquaredTest PHP Méthode

    public static function chiSquaredTest(array $observed, array $expected)
    {
        // Arrays must have the same number of elements
        if (count($observed) !== count($expected)) {
            throw new Exception\BadDataException('Observed and expected must have the same number of elements');
        }
        // Reset array indexes and initialize
        $O = array_values($observed);
        $E = array_values($expected);
        $n = count($observed);
        // number of terms
        $k = $n - 1;
        // degrees of freedom
        $χ² = 0;
        /*
         *        (Oᵢ - Eᵢ)²
         * χ² = ∑ ----------
         *            Eᵢ
         */
        for ($i = 0; $i < $n; $i++) {
            $χ² += ($O[$i] - $E[$i]) ** 2 / $E[$i];
        }
        $p = ChiSquared::above($χ², $k);
        return ['chi-square' => $χ², 'p' => $p];
    }