static public function x2(array $ngram, int $totalNgrams) : float
    {
        $var = self::setStatVariables($ngram, $totalNgrams);

        $Xsquare = 0;

        $Xsquare += ( ( $var['jointFrequency'] - $var['m11'] ) ** 2 ) / $var['m11'];
        $Xsquare += ( ( $var['LminusJ'] - $var['m12'] ) ** 2 ) / $var['m12'];
        $Xsquare += ( ( $var['RminusJ'] - $var['m21'] ) ** 2 ) / $var['m21'];
        $Xsquare += ( ( $var['n22'] - $var['m22'] ) ** 2 ) / $var['m22'];

        return $Xsquare;
    }