If you don't have the php_stats library, you can use this implementation: public static function getSkewness( $values ) { $numValues = count( $values ); if ( $numValues == 0 ) { return 0.0; } // Use function from php_stats library if available if ( function_exists( 'stats_skew' ) ) { return stats_skew( $values ); } $mean = array_sum( $values ) / floatval( $numValues ); $add2 = 0.0; $add3 = 0.0; foreach ( $values as $value ) { if ( ! is_numeric( $value ) ) { return false; } $dif = $value - $mean; $add2 += ( $dif * $dif ); $add3 += ( $dif * $dif * $dif ); } // foreach values $variance = $add2 / floatval( $numValues ); return ( $add3 / floatval( $numValues ) ) / pow( $variance, 3 / 2.0 ); }