A typical fatal incident involves a high speed collision with a tree or another person and trauma to the head is a common factor. Sadly, the evidence that a helmet can mitigate in such circumstances is lacking. Death rates have not come down with increasing helmet use and in fact, more than half of the people involved in fatal ski area accidents in the United States last season were wearing a helmet at the time of their accident.

Unfortunately, in the event of a high speed collision, the forces involved usually far exceed the protective capabilities of even the best ski helmet. There is evidence that helmets may in fact promote a false sense of security - a higher percentage of those who wear helmets travel faster and admit to taking risks than those who do not.

But helmets do seem to make a difference in the head-injury statistics: Mr. Shealy’s own research found a 35 percent reduction, and he said that other studies had found as much as a 50 percent reduction in head injuries.

“Typically, in the scenario that results in death, you need something more than a helmet to save you,” Mr. Shealy said. Referring to helmet-wearing, he said, “Where it really comes into play is if you fall into hard-packed snow,and that can turn a serious head injury into a minor injury.”