It's not enough to know rates. If you know incidents per day, but don't know hours driven per day, you can't compare safety of two modes of driving. One mode mi

It's not enough to know rates. If you know incidents per day, but don't know hours driven per day, you can't compare safety of two modes of driving. One mode might just be parked more often, and that's why it has fewer incidents per day. Similarly, if you know interventions per mile, but don't know miles of challenging circumstances per mile, you can't compare two modes. Maybe people only turn self driving on in particular circumstances. Or maybe tesla opened the beta to people in easy locations. Apples to apples safety comparisons require a lot of detailed data when they aren't part of a randomized trial (which is still hard to do correctly).