public function get_coefstring() {
        $parent_category = $this->load_parent_category();
        if ($this->is_category_item()) {
            $parent_category = $parent_category->load_parent_category();
        }

        if ($parent_category->is_aggregationcoef_used()) {
            return $parent_category->get_coefstring();
        } else {
            return false;
        }
    }