Wearing a bicycle helmet substantially reduces your risk of injury in an accident, unless the helmet is designed deficiently and fails to protect your head upon impact. A study by the Insurance Institute for Highway Safety rated bicycle helmets, and found that all helmets do not offer the same level of injury protection. Some helmets seem to do a much better job of protecting the head, compared to others.
The Insurance Institute for Highway Safety collaborated with the Virginia Tech Helmet Lab to create a bicycle helmet rating system that the two organizations claim is the first such rating system for helmets. The rating system assigned stars to each helmet based on its effectiveness against injuries.