Here's where I got that figure from:
http://www.ama-assn.org/ama/pub/article/2036-2526.html
I was a surprise to me as well. I've nothing against helmets, I own one, I don't mock people for wearing them, I'd just like to see real, non-ancedotal, evidence of their effectiveness - because most of the situation I worry about, they wouldn't be based on the evidence I've seen.