[…] Financial economists Campbell Harvey, Yan Liu, and Heqing Zhu, in a working paper posted this week by the National Bureau of Economic Research, count up the economic studies claiming to have discovered a clue that could have helped predict the asset returns. Given how hard it is supposed to be to get an edge on the market, the sheer number is astounding: The economists list over 300 discoveries, over 200 of which came out in the past decade alone. And this is an incomplete list, focused on publications appearing in top journals or written by respected academics. Harvey, Liu, and Zhu weren’t going after a bunch of junk studies.
So how can they say so many of these findings are likely to be false?
To be clear, the paper doesn’t go through 300 articles and find mistakes. Instead, it argues that, statistically speaking, the high number of studies is itself a good reason to be more suspicious of any one them. This is a little mind-bending—more research is good, right?—but it helps to start with a simple fact: There’s always some randomness in the world. Whether you are running a scientific lab study or looking at reams of data about past market returns, some of the correlations and patterns you’ll see are just going to be the result of luck, not a real effect. Here’s a very simple example of a spurious pattern from my Buffett story: You could have beaten the market since 1993 just by buying stocks with tickers beginning with the letters W, A, R, R, E, and N.