30 year returns of "ANY" period in history is surprisingly consistent.

30 year returns of "ANY" period in history is surprisingly consistent. 

The chart on left shows a huge run up after recession worries abated in Mach 2009. 1 year volatility is very high but 30 year returns are consistent & volatility low.
Periods of good returns always follow bad & bad follows good.

Reversion to mean


The professors don’t disagree that, historically, the stock market’s returns over various 30-year periods have been surprisingly consistent. Periods of particularly good returns have been followed by subpar ones, and vice versa — a process that statisticians call reversion to the mean. Prof. Jeremy Siegel, also of Wharton, and the author of “Stocks for the Long Run,” is often credited with demonstrating that mean reversion has been at work in the American stock market since 1802.



Working paper : t the University of Chicago Booth School of Business, and Robert F. Stambaugh, a finance professor at the Wharton School of the University of Pennsylvania. A copy is athttp://ssrn.com/abstract=1136847.