public function getPercentShipped(){
        if (isset($this->data['NumberOfItemsShipped']) && isset($this->data['NumberOfItemsUnshipped'])){
            $total = $this->data['NumberOfItemsShipped'] + $this->data['NumberOfItemsUnshipped'];
            
            if ($total == 0){
                return 0;
            }
            
            $ratio = $this->data['NumberOfItemsShipped'] / $total;
            return $ratio;
        } else {
            return false;
        }
    }