It's not as precise as I'd like, but there has been an independent investigation of the safety of Autopilot. After the first fatality while on Autopilot, the US National Highway Traffic Safety Administration wanted to determine whether (as many fear) Autopilot posed a danger to drivers, and found that Autopilot was safe enough to keep on the roads and that Autopilot led to a 40% reduction in crashes: https://techcrunch.com/2017/01/19/nhtsas-full-final-investig...