CAPE ratio

The cyclically adjusted price-to-earnings ratio, commonly known as CAPE,Shiller P/E, or P/E 10 ratio, is a valuation measure usually applied to the US S&P 500 equity market. It is defined as price divided by the average of ten years of earnings (moving average), adjusted for inflation. As such, it is principally used to assess likely future returns from equities over timescales of 10 to 20 years, with higher than average CAPE values implying lower than average long-term annual average returns.

Thus,

CAPE Ratio:

Value investors Benjamin Graham and David Dodd argued for smoothing a firm's earnings over the past five to ten years in their classic text Security Analysis. Graham and Dodd noted one-year earnings were too volatile to offer a good idea of a firm's true earning power. In a 1988 paper economists John Y. Campbell and Robert Shiller concluded that "a long moving average of real earnings helps to forecast future real dividends" which in turn are correlated with returns on stocks. The idea is to take a long-term average of earnings (typically 5 or 10 year) and adjust for inflation to forecast future returns. The long term average smooths out short term volatility of earnings and medium-term business cycles in the general economy and they thought it was a better reflection of a firm's long term earning power.

Shiller later popularized the 10-year version of Graham and Dodd's P/E as a way to value the stock market. Shiller would share the Nobel Memorial Prize in Economic Sciences in 2013 for his work in the empirical analysis of asset prices.

Using market data from both estimated (1881–1956) and actual (1957 onward) earnings reports from the S&P index, Shiller and Campbell found that the lower the CAPE, the higher the investors' likely return from equities over the following 20 years. The average CAPE value for the 20th century was 15.21; this corresponds to an average annual return over the next 20 years of around 6.6 per cent. CAPE values above this produce corresponding lower returns, and vice versa. In 2014, Shiller expressed concern that the prevailing CAPE of over 25 was "a level that has been surpassed since 1881 in only three previous periods: the years clustered around 1929, 1999 and 2007. Major market drops followed those peaks" (ref 4).

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