mean reversion
The theory that asset prices and returns tend to move back toward their long-term historical average over time after periods of extreme deviation.
Example
“After the dot-com bubble, P/E ratios reverted to mean — extremely overvalued stocks crashed back to historical norms.”
Memory Tip
MEAN REVERSION = what goes too far UP comes back DOWN — and vice versa. Everything reverts to average.
Why It Matters
Understanding mean reversion helps investors avoid panic selling during market downturns or getting overconfident during rallies. By recognizing that extreme price movements tend to correct over time, you can make more rational decisions about when to buy, sell, or hold your investments rather than reacting emotionally to short-term volatility.
Common Misconception
Many people mistakenly believe that mean reversion guarantees profits or that an asset that has fallen significantly is guaranteed to bounce back quickly. However, mean reversion is a tendency over long periods, not a certainty, and the reversion process can take years or may never occur if fundamental business conditions have permanently changed.
In Practice
Consider a stock trading at 50 dollars when its historical average price over 20 years is 60 dollars. A mean reversion investor might view this 17 percent discount as an opportunity to buy, anticipating the price will eventually return toward 60 dollars. However, if the stock stays depressed for two years before recovering, the investor must have patience and conviction that the reversion will eventually occur based on historical patterns.
Etymology
MEAN (average) REVERSION (returning to). The tendency to REVERT (return) to the MEAN (average).
Common Misspellings
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