Stock market data used in my book, Irrational Exuberance [Princeton University Press 2000, Broadway Books 2001, 2nd ed., 2005] are available for download, U.S. Stock Markets 1871-Present and CAPE Ratio. This data set consists of monthly stock price, dividends, and earnings data and the consumer price index (to allow conversion to real values CAPE based on data from economist Robert Shiller's website, as of 8/4/2015. The 26.45 measure was 93rd percentile, meaning 93% of the time investors paid less for stocks overall relative to earnings. Robert Shiller first proposed a ten year timeframe for his CAPE ratio, targeting it towards the S&P 500 – the most well known American stock index. Subsequently, CAPE has been adapted for a number of other countries and indexes. The Shiller PE is a valuation measure, much like its cousin the price to earnings ratio.