> ## Documentation Index > Fetch the complete documentation index at: https://docs.chicago.global/llms.txt > Use this file to discover all available pages before exploring further. # Mean Reversion > Understanding mean reversion - a tendency for a series to move toward a stable reference level, and when that tendency does and does not apply Mean reversion describes a tendency for a series to move toward a stable reference level over time. Its relevance depends on the series, measurement window and economic regime. ## Beginner ### What It Means For a mean-reverting series, unusually high or low readings tend to move back toward a reference level over time. Volatility returning toward typical levels after a temporary spike is one example. The relevant reference level can change as market conditions change. ### Example Suppose a real exchange rate is well above its historical average. A mean-reversion analysis asks whether the forces supporting its longer-run level remain stable and whether past deviations have tended to unwind. That assessment informs the outlook alongside current fundamentals and momentum. ### Why It Matters Mean-reversion analysis helps assess whether recent conditions are likely to persist. It provides context for extrapolating a trend by examining the stability of the reference level and the behavior of past deviations. *** ## Advanced ### How to Read It The reports discuss mean reversion when interpreting currencies and sentiment, often alongside [z-scores](/glossary/z-score). A z-score measures the distance from a historical mean. To assess the outlook, consider the economic anchor, evidence of reversion and the horizon over which it has occurred. ### Common Misreadings * **Applying it everywhere**: not every series has a stable reference level. Equity index levels trend upward over long horizons, so reversion logic applies poorly to them; valuation ratios and real exchange rates are more plausibly anchored, and mean-reversion analysis is more informative there * **Using it as a timer**: the speed and likelihood of reversion depend on the process; a large deviation alone does not identify an entry point * **Confusing it with contrarianism**: mean reversion is a statistical property of a series; contrarianism is a stance, the reports use the former to calibrate expectations, not to reflexively fade every move ### The Tension With Momentum Mean reversion and [momentum](/glossary/momentum) describe different aspects of market behavior and can coexist across horizons. Read evidence of a continuing trend alongside the distance from longer-run reference levels, and assess whether the economic forces behind each remain relevant. ### Related Terms Measuring the stretch The countervailing force Variability and its persistence