April 1, 2011

Thoughts On That Helmet Article…

Thoughts On That Helmet Article...

An article in Ski Canada Magazine examining helmet use stats in the US is generating quite a bit of buzz right now in the ski world. I've read the article and given it some thought, and my impression is that it's easy to misread and/or misinterpret the article's conclusions. Let's take a closer look at what the authors wrote:

The article's bombshell observation is that an analysis of raw data from a US ski area from 1991 to the present (?) indicates the rate of skier fatalities has remained relatively constant despite a significant increase in the percentage of riders who wear helmets. The obvious inference here is that helmet use has therefore not had any positive impact on skiing safety—but hold that thought!

The authors also cite a study indicating that (1) there is no advantage to wearing a helmet in soft-snow collisions; (2) in hard-object collisions (ie, trees), a helmet significantly reduces harmful forces to the brain, but collisions remain fatal due to associated trauma to other parts of the body; and (3) in hard-snow collisions, helmets significantly reduce harmful forces to the brain—potentially enough in some situations to reduce or prevent actual brain injury.

What are we to make of this?

First of all, anytime you see a statistical analysis in any literature, you should automatically be skeptical of its validity. For the short explanation of why this is so, it's because statistics is a complex field that is really, really hard to get right—even for experienced statisticians. For a more in-depth exploration of this fascinating subject, see The Drunkard's Walk (highly recommended). So let's reconsider the article's evidence, which seems to indicate helmet use hasn't had any impact on skier fatalities.

What leaps out at me is that during the time period in which the article's data was collected, the sport of skiing was undergoing a period of explosive change. In other words, the analysis does not control for other variables. For example, 1991 roughly corresponds to the arrival of terrain parks in US ski areas. Presumably, terrain parks have made skiing much more dangerous, so maybe helmet use has prevented a big spike in skier fatalities.

Alternately, consider that 1991 corresponds roughly to the arrival of shaped skis, which have made skiing much, much easier and therefore presumably much safer. So maybe helmet use has caused a big increase in skier fatalities, luckily counterbalanced by modern ski technology. There you have it: two exactly opposite conclusions drawn from the same data set.

And one last observation: looking at skier fatalities alone tells us absolutely nothing about the incidence of permanent or otherwise debilitating brain injuries suffered during the study's time frame, which, given modern medical advances in keeping head trauma cases alive (post-Iraq), could be the single most important metric of all.

My take is that any conclusion based on the apparent lack of correlation between helmet use and skier fatalities is hasty at best. If you are currently wearing a helmet when you ride, I see no reason here to stop wearing your helmet. Conversely, if you do not wear a helmet, I find no conclusive evidence here (or elsewhere) suggesting you should start wearing one. Yes, the one clear finding of the various studies cited is that helmets offer a significant reduction of harmful brain forces in most collisions. But it's just not clear whether or not that translates into a meaningful benefit for real skiers in the real world.

As the Ski Canada Mag article's author emphasizes, skiers and snowboarders need to be aware of what helmets can and can not protect against. Hard-object collisions at typical skier speeds will often be fatal regardless of helmet use. Hard-snow collisions (take note park riders!) would seem to be the modality in which helmets offer the greatest potential benefit. Whatever you decide, I encourage you to stay open-minded on the subject of helmet use, and avoid drawing hasty conclusions in either direction.

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When there is snow, SierraDescents is Andy Lewicky's California backcountry skiing and mountaineering website. Without snow, sierradescents becomes an ill-tempered hiking and climbing blog.

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