(Ritch) writes:

The article by Dorothy Robinson attempts to measure the efficacy (or
not) of mandatory helmet laws. It says nothing about the reduction
in risk of head injury given that an accident has occurred. These
are separate issues.

FWIW, the study showed no significant (or any at all, really)
improvement in head injury statistics after the introduction of MHL
in Australia.

Actually, the result was a increase in the risk of head injuries
because people stopped cycling in droves, which in turn made the roads
a more dangerous place to be. This has all been discussed ad
infinitum before and the archives are at Google.