This had always been my critique. The statistical techniques used never identified actual cause.It goes happily on. But allow me to remind that these studies cannot discover cause. It is always an outside assumption of what is causing the noticed reductions and increases, because why? Because the thing said to be doing the causing is never measured on individuals! Repeat that out loud, to yourself and the nearest stranger. Asserting cause in these cases is always by fiat or direct assumption—which is cheating.
http://wmbriggs.com/post/21057/