Prospective Cohort Study

Studies published in the scientific literature have consistently demonstrated that wearing a helmet while bicycling is associated with lower odds of head injury in a crash. However, there has been criticism of these studies in the media, including the assertion that these studies have overstated the protective effect of helmets. One of the most common critiques includes the frequent use of the case-control study design and limitations associated with this design. One of the primary reasons that case-control studies have been used is because head injuries attributable to bike crashes are a relatively rare event. Cohort studies, on the other hand, can provide stronger evidence due to their prospective nature, but they require far more time and resources than a case-control study, especially for rare outcomes.

Researchers enrolled 5000 head injury-free cyclists into a prospective cohort study. "Helmet use" was defined as self-reported helmet use during at least 90% of their time cycling. Once a year, participants were contacted and asked if they had a head injury due to a bike crash in the past year. All reported incident head injuries were confirmed with medical records, and only those that were confirmed were included in analysis. The participants were followed for 4 years.

HEAD INJURY INCIDENCE AMONG HELMET USERS AND NON-USERS (N=5,000) # without head Total Group # with head injury # person-years during follow-up injury during follow- observed during follow- up up Helmet Users 152 3,598 3750 13,688 Helmet Non-Users 163 1,087 1250 3,375