protected function col_random_guess_score($questionstat) {
        if ($this->is_calculated_question_summary($questionstat)) {
            list($min, $max) = $questionstat->get_min_max_of('randomguessscore');
            return $this->format_percentage_range($min, $max);
        } else if (is_null($questionstat->randomguessscore)) {
            return '';
        } else {
            return $this->format_percentage($questionstat->randomguessscore);
        }
    }