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On Wed, 19 Jul 2006 12:00:25 -0400, Mann, Dave <[log in to unmask]> wrote:

>> The average speed for helmet users of
>> 45.8 km/h (28.4 mph) was significantly higher than those not using a
>> helmet at 41.0 km/h (25.4 mph).
>
>This is not surprising to me at all.
>

Isn't it also likely that there's a bit of selection bias going on here?  
In my experience, most of the experienced skiers I know are aware of the 
dangers of skiing w/o a helmet, so they get a lif pronto.  When I ski with 
guys who are only on the hill 5-10 days/year, and are less skiled skiers, 
they don't see the need quite as much.  Good skiers are self-selecting 
into the helmet group, therefore raising their mean speed higher than 
you'd otherwise see in an apples to apples comparison.  

If you controlled for skill level and conditions, I believe the difference 
wouldn't be nearly as stark, though it would still exist to be certain.

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