I've never seen any clear evidence that they are effective against minor falls. I wear one myself, it seems instinctively the right thing to do, but the evidence just isn't there afaik.
The same logic could be used to recommend helmets for all car drivers, and for all pedestrians too.
Couldn't agree more. The only studies that I've seen that are even remotely scientific seem to indicate that you have to fall in a very specific way at a low speed, at a low impact level and on the strongest part of the helmet. The fact that it is a legal requirement in so many countries yet there hasn't actually been a full study on how effective they are is incredible.
But then the same is true of child car seats/booster seats compared to seat belts. No difference at all in safety once the child is over above 3. The difference there is that there are studies which clearly prove this point, but it's still law to have a child seat.