public function description() {
        list($missingparent, $loops) = $this->find_problems();

        $description = '<p>The course categories should be arranged into tree ' .
                ' structures by the course_categories.parent field. Sometimes ' .
                ' this tree structure gets messed up.</p>';

        $description .= tool_health_category_list_missing_parents($missingparent);
        $description .= tool_health_category_list_loops($loops);

        return $description;
    }