Jim Cramer is the eccentric CNBC analyst who gives stock picks at 6pm Mon-Fri (in a fairly wild manner). He was a former Hedge Fund Manager. How good is his investment advice against, say, a wild monkey. Click here for the surprising results.
There is actually theoretical backing for this and its called the efficient market hypothesis. The idea is related to perfect competition. Since there are so many buyers and sellers in the market that possess all necessary information about an investment (stocks, bonds etc) a professional money manager should not be able to outperform a normal buy and hold pattern of a well diversified portfolio. The evidence for this is actually quite strong.
The real kicker is what exactly do we mean by all information? Are we talking about all past price moves (the weak form), all publically available knowledge, including my predictions (the semi-strong) or all public and private knowledge (the strong form).
I think most economists would agree that most markets are either weak to semi-strong efficient markets. However, it looks like the market to predict the currenct Pope was strong form