THE surest way for motorcycle riders to avoid joining the rapidly growing ranks of fatality statistics  up 144 percent since 1997, according to the National Highway Traffic Safety Administration  is to wear proper head protection. A helmet increases the chances of survival in an accident by 37 percent, the safety agency says.

Picking the helmet that provides ideal protection is not easy, however. While all helmets sold for road use in the United States are required to carry the stamp of a federal safety standard established by the Transportation Department, riders may also find an independent certification label, from the Snell Memorial Foundation, on many helmets they are considering.

The certification by Snell, a nonprofit research and testing organization financed by helmet makers, is not mandatory for road use but it is for some racing series, which can lead consumers to assume that a Snell-compliant helmet is safer  an assumption that is not agreed upon by researchers.

Even knowing the differences between the standards is not enough: on Oct. 1, helmets meeting a new Snell test, M2010, with revised force limits, can go on sale, probably adding to the confusion among helmet shoppers.