Most studies on the effectiveness of cycle helmets using the case-controlmethod, are overestimating the effect of the helmet, says Theo Zeegers, an independent researcher and mathematician.
The risk of getting a head injury per kilometre wearing a helmet relative to the same risk without helmet is the most appropriate measure to assess the effectiveness of the bicycle helmet.
Due to lack of data on exposure rates, odds ratios of helmeted versus unhelmeted cyclists for
head injury and other injuries on hospitalized victims are broadly used in case-control studies.
A general necessary and sufficient condition can be formulated rigorously, for which odds ratios indeed equal risk ratios. However, this condition is not met in case-control studies on bicy-
cle helmets. As a consequence, the real risk of cycling with a helmet can be underestimated by
these studies and therefore the effectiveness of the bicycle helmet can be overestimated. The
central point is that a wrong estimate of the risk for non-head injuries (the controls) paradoxi-
cally can lead to an overestimation of the usefulness of the helmet in protecting against head
Meer hierover zie deze pagina van de Europeran Cyclist Federation