protected function get_regraded_questions() {
        global $DB;

        $qubaids = $this->get_qubaids_condition();
        $regradedqs = $DB->get_records_select('quiz_overview_regrades',
                'questionusageid ' . $qubaids->usage_id_in(), $qubaids->usage_id_in_params());
        return quiz_report_index_by_keys($regradedqs, array('questionusageid', 'slot'));
    }