Reblog: Mean Reversion and the Bell Curve

The pressure to outperform all the time leads stock pickers to constantly seek mean reversion trades

Over a three-year time period, stock prices tend to mean revert. This has spawned numerous investment approaches that try to squeeze capital gains out of those reversions. Classic deep value investing, as popularised by Benjamin Graham at Columbia Business School, taught that you would succeed by buying 50-cent dollars and selling them when and if they reverted to the mean. The “Dogs of the Dow” strategy of buying the 10 highest-yielding Dow stocks was born out of mean reversion.

Over long time periods, common stock performance falls on a bell curve like the one listed below. Half the stocks outperform and half underperform. Among the poorest performers, some go to 0%, and 5% of common stocks do so poorly that they can ruin a concentrated stock portfolio. (1)

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