protected function getCriterionsAverageScore(\SimpleXMLElement $rating)
    {
        $criterions = array('criterion1', 'criterion2', 'criterion3', 'criterion4', 'criterion5', 'criterion6');
        $sum = 0;
        $divider = 0;
        foreach ($criterions as $criterion) {
            $criterionValue = (float) $rating->$criterion;
            if ($criterionValue > 0) {
                ++$divider;
                $sum += $criterionValue;
            }
        }
        $divider = (0 == $divider) ? count($criterions) : $divider;

        return $sum / $divider;
    }