public static function get_non_respondents_parameters() {
        return new external_function_parameters (
            array(
                'feedbackid' => new external_value(PARAM_INT, 'Feedback instance id'),
                'groupid' => new external_value(PARAM_INT, 'Group id, 0 means that the function will determine the user group.',
                                                VALUE_DEFAULT, 0),
                'sort' => new external_value(PARAM_ALPHA, 'Sort param, must be firstname, lastname or lastaccess (default).',
                                                VALUE_DEFAULT, 'lastaccess'),
                'page' => new external_value(PARAM_INT, 'The page of records to return.', VALUE_DEFAULT, 0),
                'perpage' => new external_value(PARAM_INT, 'The number of records to return per page.', VALUE_DEFAULT, 0),
                'courseid' => new external_value(PARAM_INT, 'Course where user completes the feedback (for site feedbacks only).',
                    VALUE_DEFAULT, 0),
            )
        );
    }