Some readers here may be familiar with NHTSA's 2004 report, Helmet Effectiveness Revisited (300K PDF), which repeated, with more recent data, a 1989 analysis that estimated lives saved by motorcycle helmets. Specifically, it answered the question: What percentage of unhelmeted motorcyclists killed would live if they wore helmets? The conclusion was that 37% of unhelmeted deaths could be prevented.

The rather clever analysis used NHTSA's FARS database to look at thousands of motorcycle crashes over 10 years that involved both a rider and a passenger, at least one of whom died. By dividing cases into the four combinations of helmet use—neither helmeted, both helmeted, rider only, passenger only—they could compare, for example, the fates of helmeted and unhelmeted riders when the passenger was helmeted. Results of the comparisons were then combined to produce the overall estimate of 37% effectiveness.

Because science is never "finished," it is desirable to re-test even well established results using new methods. If the result differs, it might indicate a problem in the earlier method (or in the new). But if the new method produces a similar result, it strengthens the original conclusion. Though the data needed to estimate helmet effectiveness is hard to find, I recently came upon another source from which the calculation can be made—and in a different way

The data comes from the State of Ohio's Department of Public Safety. In their annual "Traffic Crash Facts" publication, DPS reports both helmet usage and injury status (fatal, non-fatal, uninjured) of all motorcycle crash victims. Combining totals for the 12 years of available data—more than 40,000 victims—I found that 3.746% of unhelmeted riders died while 2.217% of helmeted riders died. That's a 40.8% lower death rate among helmeted riders, very close to the 37% lower rate predicted by NHTSA's estimate.

This isn't a groundbreaking discovery; it only confirms what was already known. But I did find it interesting that an independent data set produced an estimate so close to NHTSA's.

The 1994-2005 editions of Ohio DPS's "Traffic Crash Facts" are downloadable as PDFs from this page.