Famed Yale Economist Robert Schiller invented the CAPE, which measures the inflation-adjusted average P/E ratio of the last 10 years, as an improved tool for determining when the market becomes overvalued. The result of nearly three years of a correction-less bull market is a cyclically adjusted P/E ratio ( CAPE ) of 25.53. Historically, the median CAPE of the market since 1870 has been 15.93.