/**
  * prepare collection
  *
  * @return Varien_Object
  */
 protected function getPreparedCollection()
 {
     //all active subscribers
     $collection = $this->_getCollection();
     $totalSubscribers = $collection->getSize();
     //all active subscribers who are also customers
     $customerSubscribers = $collection->addFieldToFilter('customer_id', array('neq' => '0'));
     $customerSubscriberCount = $customerSubscribers->getSize();
     $days = $this->calculateOperationalDaysFromOrder();
     if ($days) {
         $subscribersPerDay = number_format($totalSubscribers / $days, 2);
     } else {
         $subscribersPerDay = $totalSubscribers;
     }
     $resultObject = new Varien_Object();
     $resultObject->setTotalSubscriber($totalSubscribers)->setTotalSubscriberCustomer($customerSubscriberCount)->setSubscribersPerDay($subscribersPerDay);
     return $resultObject;
 }