public function getSum(
        $sortByMetric = 'delivered',
        $sortByDirection = 'desc',
        $limit = 5, $offset = 0
    ) {
        $this->validateOptions(
            'sortByDirection',
            $sortByDirection,
            self::OPTIONS_SORT_DIRECTION
        );
        $this->validateInteger('limit', $limit);
        $this->validateInteger('offset', $offset);
        $stats = $this->getGlobal();
        $stats['sort_by_metric'] = $sortByMetric;
        $stats['sort_by_direction'] = $sortByDirection;
        $stats['limit'] = $limit;
        $stats['offset'] = $offset;
        return $stats;
    }