English Dictionary

There are several ways to approach predictability. One way is to investigate whether asset prices over the past few days or weeks can be used to predict tomorrow’s price. The answer is no. Following a large amount of careful statistical work by Fama in the 1960s, researchers now agree that past prices are of very little use in predicting returns over the immediate future. … An implication of the excessive swings in stock prices is that a high ratio of price relative to dividends in one year will tend to be followed by a fall in prices relative to dividends over subsequent years, and vice versa. This means that returns follow a predictable pattern in the longer run. Shiller and his collaborators demonstrated such predictability in stock markets as well as bond markets, and other researchers have later confirmed this finding in many other markets.