The Mercatus team also took into account that the Academy of Model Aeronautics (AMA) found last year that the FAA recorded even simple drone sightings as a "near miss." If you'll recall, the decision to require drone owners to register machines weighing more than 250 grams (.55 pounds) was based on fears that the UAVs could put planes at risk. Apparently, though, out of the 764 reported incidents, only 27 were actual near misses.
Based on all these information, the group concluded that it will take 1.87 million years of flight time for a lone 2kg (4.41 pounds) drone to damage an aircraft. Further, it will take 187 million years of flight time for a UAV to cause injury to a passenger on board. On the other hand, they do acknowledge a lack of data on exactly what kind of damage a UAV can cause, since turbines are only tested to see how they'll handle bird strikes. We doubt this study will make the FAA reconsider the compulsory registration, but if it does, then raising the size limit required for registration may be a good start.