Like SK, my only needed approved test was when I was thrown from my bike at 17 mph (thank you, tire eating road gap). The major crack on the helmet, and the fact that I didn't suffer any head injuries (no headache- nothing) tells me that helmets work. And I went down HARD- head first.

I don't need no stinkin' scientific studies to make me wear one. Common sense tells me that my skull is only so strong and any blunt force to it will cause injury- therefore wearing a helmet that may absorb said force and prevent my skull from cracking is a good thing.