I’m saying that the ability of a helmet to reduce injury in crashes with motor vehicles is negligible, as evidenced by the failure of widespread or mandatory use of helmets to reduce the rate of cyclists killed or seriously injured.
The simple problem is that an F-150 doing even a moderate 40mph imparts far more energy to you than can be absorbed by an inch of styrofoam.
Studies based on emergency room observations (which is most of the studies in that Cochrane meta-study) tend to lump all crashes together, which makes helmets look far more effective than they really are because of course you don’t get the minor scalp wounds helmets are designed to prevent if you’re wearing one.
