In terms of market calls, few academics or economists can match Yale University economics professor Robert Shiller. In his 2000 book, Irrational Exuberance , he argued that 10-year averages of corporate earnings smoothed out the ups and downs of the business cycle. Then, using this "cyclically adjusted" level of earnings and comparing it to current stock prices, he claimed to generate a better version of the P/E ratio. Shiller's timing couldn't have been better. The "Shiller P/E ratio" was at an all-time high in 1999-2000, a clear signal of overvaluation and a reason to sell.Today, Shiller's valuation work says that stocks are back to being in overvalued territory. At the end of July, Shiller's ratio was 23.8, the highest since 2008.