The cyclically-adjusted price-to-earnings ((CAPE)) ratio is a surprisingly controversial metric, but evidence suggests it is actionable for long-term investors.
Rather than simply dividing the current share price by 1 year of earnings like the normal P/E ratio, the CAPE ratio divides the current price by the past 10 years of inflation-adjusted earnings. It gives you a better idea of how cheap a stock or a market of stocks is relative to a full business cycle of earnings rather than potentially one year of peak or trough earnings.
This metric was popularized by Yale professor Robert