Historic P/E of Stocks

Looking at the historic P/E chart of S&P 500 we see that something strange happened around 1980. Prices of stocks started to go up without ever again correcting down under the historic average of 15. While the historic average P/E rate was about 15 before 1980, the average has since been well above this, and 15 has been a bottom.

Keeping in mind that central banks have been increasingly involved in price manipulation and purchase of stocks since 1980, we can assume that what we are seeing is a central bank induced bubble that will eventually pop, in which case we will again see P/E rates well below 15. However, it is impossible to say how much longer the bubble can be sustained. It may still be decades before we see a return to free and fair pricing of the stock marked.

http://www.macrotrends.net/2577/sp-500-pe-ratio-price-to-earnings-chart