The "countermeasure for head protection" should not be based on "average thickness" of the skull, but on the "minimum thickness", should it not? For both male and female. It should provide protection in the worst case.
I wonder, if and how the minimum thickness differs between males and females.

hahahahahahahaha, oh how I luv u wildcat.

Ha ha ha! In Ireland, if yer ma says your thick....yeh probably are!