I do not have "data" to support the comment. As
@Sadlsor mentioned, I know that several countries have tiered levels of licensing which lets drivers move up to the next level of license as their skills merit. I believe that they also pay a fair bit for lessons, monitoring, etc. as they work their way towards their full license. Someone in Switzerland once told me the equivalent of $2,000 - $3,000 (haven't confirmed that).
There is no question in my mind that European drivers (at least where I ride in the Alps) are much better in general than American drivers. They are able to drive quicker without wandering into oncoming traffic, they are more polite, use their directionals, etc. and do so on tighter, twistier roads. Cell phones are still mostly prohibited and enforced - same for alcohol consumption. I feel MUCH safer riding a motorcycle over there than I do here.
I would also say that riders who come on my Alps tours for 7, 10, 14 days etc. riding all day every day in the Alps, with all their switchbacks, sweepers, elevation changes, "brisk" riding speeds, etc. all feel that they are riding better at the end of the tour than when the arrived simply because of the nature of the riding. That is certainly true for me. I suspect that if you live there and ride there all time that the riding environment there translates into a more skilled rider.