public static function get_non_respondents_returns() {
        return new external_single_structure(
            array(
                'users' => new external_multiple_structure(
                    new external_single_structure(
                        array(
                            'courseid' => new external_value(PARAM_INT, 'Course id'),
                            'userid' => new external_value(PARAM_INT, 'The user id'),
                            'fullname' => new external_value(PARAM_TEXT, 'User full name'),
                            'started' => new external_value(PARAM_BOOL, 'If the user has started the attempt'),
                        )
                    )
                ),
                'total' => new external_value(PARAM_INT, 'Total number of non respondents'),
                'warnings' => new external_warnings(),
            )
        );
    }