I'd love to see a one place study on increase/decrease of institutional, hedge fund, and sovereign wealth fund trading. And match that to money flow threw-out the investemnt vehicles available. Because it's big money which causes (manipulates) national exchange direction.
I fooled with this a little back in late 2007, early 2008. when I expected the crash. Noticed big guys selling equities and buying metals, to back my long term chart projections. A real lot of work, because you can't find one spot for all the info. But the work helped me make my decision to STOP trading for a year in April, a month before the crash. And get back in just after the March 2009 bottom bounce.