I live in an area with roundabouts. The frequency of collisions actually seems higher because people do not know the rules and do not yield before entering the roundabout.
I live in an area with roundabouts. There are very few accidents in roundabouts and it's impossible to get a license if you don't know how the rules for a roundabout.
What the studies say is; "they can substantially reduce crashes that result in serious injury or death." That is not the same as a reduction in the total number of accidents. The number of accidents may actually be higher in a roundabout, but the severity is lower and they are more survivable.