Very interesting, so there are a few studies! Thank you for pointing this out, I had been under the impression that there were none whatsoever. I am not sure what conclusions can be drawn from these few studies at present (I found four or five on the Google Scholar link). It would be interesting if someone with the requisite technical background could read and assess them. (And the question of funding, as discussed in the Guardian article I linked to in another post, is also relevant, as empirically speaking, industry-funded studies on the whole do lead to significantly different results from independently-funded studies).