Two more anecdotes to add to the stories, both are about big guys, over 6 feet and 200 pounds.
The first was not on a bicycle, but on inline skates. One of the guys who used to go on the Friday Night Skate with us was a frequent skater on the Monona path. He never wore a helmet until he met some experienced speedskaters who told him lots of stories about falls they had taken, in spite of being excellent skaters. So he started wearing his helmet.
Only a week or two later, he was coming up to the Monona Terrace behind some pedestrians, and called out "on your left!" before he passed them. One idiot moved TO the left, and Tom hit him and went down hard, cracking his helmet in about 3 places. A chunk of the helmet on the left rear had completely broken free, held on only by the helmet straps. Tom didn't even have a concussion. it was pretty obvious from looking at the helmet that Tom would have been very badly hurt without the helmet.
The 2nd story is about my sister's late husband. While Mike did die while on a bicycle, it wasn't due to lack of a helmet, his heart gave out while going up a long ascent in Oregon.
But a month or so before that he was riding back from errands on his nice Ciocc road bike, which had after-market aero bars attached to the handlebars. One aero bar suddenly came loose and dropped into the front wheel, stopping it instantly. Mike went down *hard* onto the asphalt, shattering the front of his helmet. He also banged up his face a bit, but the helmet definitely saved his life that time.
I don't know what to think about all the various studies. My gut feeling is that helmet laws don't actually lead to more people using helmets for casual riding, and that anybody who would use a helmet for training or touring already would have been using one. Do any of the studies actually measure how many people are wearing helmets, vs. just citing helmet laws?