By Charles Pekow
It reported that 13 studies found that helmet laws don't reduce riding, eight reported mixed results and two said they did — but only in certain circumstances. In Australia, for instance, fewer children were seen biking to work when required to wear helmets — but that likely resulted from other factors, such as an increase in busing and even a New Zealand campaign to discourage kids from riding.
Regarding taking increased risks, a review of 22 studies found 17 said helmets don't encourage dangerous behavior, three found pro and con evidence and only two supported the thesis. But the studies contain some limitations: some dealt with risky behavior in general, not entirely bicycling.
Reference: Bicycle Helmets: Systematic Reviews on Legislation, Effects of Legislation on Cycling Exposure & Risk Compensation: https://www.trafikverket.se/contentassets/d799726f68ec49f69466f08e533b1f30/bhl_systematic_review_final.pdf; Olivier et al., UNSW Sydney.