The research is available and has been for decades. It's very basic and not technically complicated. As previously stated, "they've discovered the obvious".
What the current crop of #*&$@#*&$s in Washington and Virginia choose to do with this information is a another subject.
As a combat veteran whose life (literally) was saved (literally) by his helmet, I discovered this organization and I offer you this;
http://www.operation-helmet.org/history.htmlI suppose there are much more important things to spend the lousy fifty-five bucks on ...................
Subject-related but off-topic rant complete ...... sorry ....... back to your original programming.
DS