There are plenty of studies, the problem with them is that there are arguments made <i>constantly</i> that despite the efficacy of helmets in reducing the severity of head trauma, something about the helmets somehow makes them more dangerous.<p>I think my favorite stupid argument though is that it increases the size of the rider&#x27;s head, which increases the likelihood of ground collision in an accident. As though it&#x27;s <i>so</i> easy to stop yourself from falling as long as there aren&#x27;t two inches of material strapped on your noggin.<p>The basic fact is that if you <i>do</i> have a head injury on a bike, a helmet is likely to reduce the severity of it. Everything else is an unquantifiable argument about human behavior.