Proof that most methods of making stock market predictions don’t work

[5/19: fixed the pdf link]
Summary of a Vanguard study:
http://monevator.com/methods-of-making-stock-market-predictions-dont-work/
Link to the study:
https://personal.vanguard.com/pdf/s338.pdf

Note that the methodology is applied only to predicting whole market returns: it isn't applied to choosing individual stocks.

Money quote: "... most of the variables they studied were about as helpful as asking your dog for one bark or two to tell you whether the market was headed up or down."

And some discussion about application of the approach to individual stocks here
http://www.bogleheads.org/forum/viewtopic.php?t=66143