Studies that show boxing headgear is no good?

Can anyone point to studies that show that boxing headgear either does not prevent concussion or in fact makes it worse?

I've found headgear to cause problems for me, and I've heard from expert boxers that it's useless or harmful, but non-boxers treat these conclusions like pure idiotic myth. I've even asked Mythbusters to test it, but I got laughed off their forums for saying something that "clearly flies in the face of all known physics." I'd love to have see some science to back up what experienced boxers have found.

This was just on news, said that helmets don't do much good. I'd guess better than nothing..but not make it "safe"

Its funny , as a kid in the UK your made to fight in head gear , yet we never did nor do i today spar in it lol