December 27 The Shiller P/E, the ratio provides the average inflation-adjusted earnings for the S&P 500 (the SPX) over the previous 10 years. Its 20th-century average has been 15.21. Only four times in the last 100 years has the Shiller P/E been above 25. Those times were 1929, 1999, 2007, and now. We all know what came next after the market peaks in those years. Those times were just before the Great Depression, before the DOTCOM bubble collapsed, before the Liar Loan mortgage derivatives collapsed and right now. Coincidentally they were all long bull runs. But some fools say we are in a new 40 year bull market and that we have a long way to go.

http://www.multpl.com/shiller-pe/

http://finance.yahoo.com/news/must-know-shiller-p-e-130033217.html

http://www.investopedia.com/terms/p/pe10ratio.asp