Fairly recent study (2011) that I'd not seen from Aussie-Stralier that discusses the levels of protection actually found for various pieces of protective riding gear. I was surprised to see how badly cheap gear fared in this. There are also some really good references at the tail end.
http://www.georgeinstitute.org/sites/default/files/documents/motorcycle-protective-clothing-protection-from-injury-or-just-the-weather-the-gear-study.pdf
http://www.georgeinstitute.org/sites/default/files/documents/motorcycle-protective-clothing-protection-from-injury-or-just-the-weather-the-gear-study.pdf