@RND First: all you need to do is look at the Refences section to start to see a good cross-section of the helmet studies done. That begins to tell you the amount of research out there. Then you read the references and their included references, building up a list of keywords to then do a literature search using databases such as IEEE and NCIB etc.
Do you tell your mechanic that he doesn’t know what he is talking about when they may say, “Your truck needs new fuel injectors due to a spooling issue?” How is my expertise any more in question?
Second: the conclusion was hair has NO EFFECT on friction between the scalp and hair. In other words, helmet testing done on naked head forms is valid. COF means Coefficient of Friction. COF is actually how helmets work! You need a high COF to hold the helmet in place so the impact forces are dissipated in the liner and not in your brain.
Third: the study found the hair significantly REDUCES COF between the helmet and scalp, meaning that thick mats of hair as what hunters do when tucking their hair up, makes the helmet more likely to slip and the impact forces transferred to the brain.
Nobody noticed that one of the authors on this paper was the CEO of Charles Owens!! Roy Burek was a good engineer and was very devoted to safety and efficacy of the CO product.