Bicycle Helmets: Systematic Reviews on Legislation, Effects of Legislation on Cycling Exposure, and Risk Compensation.
This study out of the University of New South Wales in Australia suggests that:
The current debate around bicycle helmet legislation and, more generally, bicycle helmet use is complex, divisive and emotive. Two major arguments are that introducing bicycle helmet legislation will reduce cycling and that wearing a helmet will increase risky behaviours thereby offsetting the safety benefit offered by the helmet. The systematic reviews detailed in this report do not support either of these arguments.