Statistically, I don't know...Haven't checked here...
I know many of my friends still refuse to wear them...Chances of being stopped are minimal, and the fine isn't really a deterrent..I have friends that were saved by them...and those that would most likely have died had they been wearing them...
Many feel it's a government intrusion, and won't wear them on principle alone...Still others feel it just makes it easier to recover the bodies....
Personally, I always wear mine...Not because it's law...I just always felt safer, and got into the habit long before it was even required..