S&P 500 Fair Value (Based on Fwd-Earnings)
When interest rates were between 4% and 6% in the timeframe 1955 until the year 2014, the stock market traded at an average P/E of 20.4x (P/E = Price-Earnings Ratio). If you put standard deviation bands around the cluster, the range would...
...be 16.6x - 26.6x for one standard deviation.