IF you’ve been wondering whether it’s possible to regularly beat the stock market averages — a natural question with the market at an all-time high — you didn’t get any guidance from the Nobel Prize committee this year: Two of the winning economists disagree on that perennial issue.

In one corner is Robert Shiller, the Yale economist who argues that markets (and by implication, share prices) are often irrational and therefore beatable. He famously predicted the bubble in technology stocks in the late 1990s.

In the other corner is Eugene Fama, the father of the view that markets are efficient and that they are always processing all available information. Mr. Fama’s followers believe that investors who try to beat the averages will inevitably fail. (There was also a third winner, Lars Peter Hansen.)

As someone whose professional life centers on evaluating investment managers, I come down emphatically with Mr. Shiller.