lg
I think one group of medics / dentists were pushing for full face helmets for that very reason.
Presumably they'd never ridden a bike themselves. Whilst a normal bike helmet is no real hardship, whatever the pros and cons, a full face one would be very unpleasant to wear. I do choose a full face helmet for riding my motorbike, and it is unpleasant when town riding in hot weather, and I'm merely sat there rather than working hard pedling
Helmet type of choice for me is a full face one. There's protection for the back and side of the head. Protection not there in with a road helmet.
It's the type that was worn at the time I was T-boned at a junction on my way home from work in 2005. The shoulder taking the major impact on the cars bonnet. The head followed through when the upper torso stopped moving. I blame the neck being flexible for allowing that to happen.
The left leg took the main impact, front of the car. Left foot still on the pedal, held in place by toeclip and strap.*
Not certain where you get the 50 - 100% figure of a helmeted head being more likely to impact than a non helmeted head though. There's too many variables in any collision to be that certain beforehand. The body will continue moving, until brought to a halt. The last part of that will often, but not always, be the head.
*If the foot had come out, there's every chance the bike and myself would have parted company, with first the bike hitting the road then me. It caused me to land firmly on the bonnet, taking the weight off the bike and lifting the bike in the process. Maybe it's a case of "A toeclip and toe strap saved my life."