Staggeringly obvious to the rest of us, but the USA seems to need this stuff pointed out to them. Following the repeal of the motorcycle helmet law in Pennsylvania, there has been a 32 percent increase in head injury deaths and a 42 percent increase in head injury-related hospitalisations.

Following the repeal in 2003, helmet use by motorcyclists involved in reported crashes decreased from 82 percent to 58 percent in the two years following.

Under the current law, only motorcyclists under 21 and riders with less than two years experience who have not taken a safety course are required to wear helmets.

"Our findings strengthen the argument for more comprehensive helmet laws that help protect riders and lower the cost of health care," said Hank Weiss, Ph.D., M.P.H., study co-author and associate professor, Department of Neurological Surgery, Center for Injury Research and Control, University of Pittsburgh.

The study is to be published in the August issue of the American Journal of Public Health