I don't have any documentation off hand, just an accumulation of information from magazine articles &c over the last 37 years.
I'll also mention that safety gear can make you less safe by distracting you, annoying you (ever try to ignore a seam that is in just the wrong place?) or blocking your view.
Every full helmet I've owned has blocked my view of the switches on the fairing and at least one required me to tilt my head down to see the instruments, not a lot but enough that my eyes were off the road ahead longer than if I was wearing an open helmet. And all of the ones I had before the GM54 blocked my peripheral vision enough that I wasn't as aware of the exact locations of other vehicles around me in heavy traffic.
Which leads to another reason for recommending a modular helmet: When you get into a situation where the blocked view could endanger you you can open the modular helmet and see better.
And speaking of other safety gear, when I took the course to get my license we were required to wear boots that at least covered our ankles. Sneakers or dress shoes were forbidden because they just aren't strong enough if you put your foot down slightly early and we were told that shoe/boot laces on a motorcycle were a really bad idea because they can come undone and get tangled in moving parts so zipper or pull on boots were best.
Over the years I've seen a lot of people on bikes wearing full helmets and sneakers, almost as if they think they don't need to protect the parts of their body that they know are going to touch the road every time they stop.
BTW: A close friend who was a motorcycle course instructor told me that steel toes weren't a good idea either because if your foot hits the road the wrong way the steel toe cap can cut your toes off.
