[matt_morgan]

"The people who wear helmets are likely more safety-conscious than those who don’t, which makes comparing the two groups very difficult and will make it appear that helmets are more protective than they actually are."

Unless the act of wearing a helmet is part of what reminds you to be more safety-conscious. Bucking my child into the car has the same effect.

BTW the author does mention that study about drivers coming closer to bikers with helmets.