The question isn’t do helmets reduce the risk of head injury, its “is that reduction worth the inconvenience given this situation”, for example for most people, walking around their own home has a low enough risk of head injury that a helmet isn’t worth it, while riding a motorcycle is, if you have anything to protect.
The total number of accidents and population in those cities helps. The fact that Denmark doesn’t have a helmet law suggests to me that people are expected to have the judgement regarding the risk they’re actually taking.
The question isn’t do helmets reduce the risk of head injury, its “is that reduction worth the inconvenience given this situation”, for example for most people, walking around their own home has a low enough risk of head injury that a helmet isn’t worth it, while riding a motorcycle is, if you have anything to protect.
The total number of accidents and population in those cities helps. The fact that Denmark doesn’t have a helmet law suggests to me that people are expected to have the judgement regarding the risk they’re actually taking.