I've never seen worldwide data, and it wouldn't make sense to have such a broad sample anyway. What I am saying isn't that experienced cyclists don't wear helmets; there are many that don't, just as many inexperienced cyclists do. But in the U.S. if you added up the total number of miles(hours) biked by each group, it wouldn't be a fair comparison, because the helmet-wearers would account for so many more hours and miles biked per person that they would still have an increased risk of head injury.

Most head injuries on hockey skates happen to people wearing hockey helmets, because the people wearing the helmets spend more time on the ice per person than do people who don't where a helmet on the ice.

I'm going to repeat myself. This type of anti-helmet/anti-safety device argument has been used in every sport and every business I can think of. The debate isn't whether helmets offer additional protection, the debate is whether people want to be bothered with wearing a helmet or what risks are they willing to accept so they don't have to wear a helmet. Anti-helmet proponents find every possible argument to justify it to themselves it isn't worth it, just as smoking addicts use every possible justification to think "smoking isn't that bad."