http://sci-hub.io/10.2466/pr0.1996.78.2.391
https://www.ncbi.nlm.nih.gov/pubmed/2616610
But there are other studies linked that seem to confirm it.
https://www.ncbi.nlm.nih.gov/pubmed/3696469
https://www.ncbi.nlm.nih.gov/pubmed/18463628
Not sure where that leaves us.
http://sci-hub.io/10.2466/pr0.1996.78.2.391
https://www.ncbi.nlm.nih.gov/pubmed/2616610
But there are other studies linked that seem to confirm it.
https://www.ncbi.nlm.nih.gov/pubmed/3696469
https://www.ncbi.nlm.nih.gov/pubmed/18463628
Not sure where that leaves us.