Half-Life Mean Reversion
Published Last updated
Key Takeaway
The time required for a mean-reverting price spread to decline by fifty percent from its maximum deviation, measuring mean-reversion speed critical for pairs trading entry/exit timing.
Learn These First
What Is Half-Life Mean Reversion?
The time required for a mean-reverting price spread to decline by fifty percent from its maximum deviation, measuring mean-reversion speed critical for pairs trading entry/exit timing.
How Half-Life Mean Reversion Works
Frequently Asked Questions
How do I use half-life calculations to improve my cryptocurrency pairs trading strategy?
Calculate half-life for each candidate trading pair using historical spread data and Ornstein-Uhlenbeck process fitting. Pairs with shorter half-lives (3-10 days) are superior because they enable faster profit realization and lower holding period risk. Use the half-life value to inform position holding duration—exit positions after approximately two half-lives to capture most mean reversion with reduced tail risk. Adjust position size inversely to half-life: shorter half-life pairs accept smaller positions with tighter margins; longer half-life pairs require larger positions with wider profit targets. Screen out pairs with half-lives exceeding forty-five days as capital efficiency drops prohibitively.
Why do shorter half-life cryptocurrency pairs outperform longer half-life pairs in mean reversion trading?
Shorter half-life pairs revert faster, enabling profit realization within shorter timeframes and reducing exposure duration to regime changes or unexpected volatility. Capital committed to shorter half-life trades turns over faster, generating higher returns per unit capital annually. Shorter holding periods mean lower opportunity costs and reduced leverage requirements. Additionally, shorter half-life regimes are typically more stable and predictable; longer half-life pairs often indicate weakening correlations or emerging non-stationarity, reducing strategy confidence. From a risk management perspective, brief exposure windows minimize accumulated slippage and market impact.
What should I do if a cryptocurrency pair's half-life changes significantly?
Significant half-life changes signal regime shifts or relationship deterioration. If half-life extends beyond historical range, investigate underlying causes: changing market correlations, reduced liquidity, or emerging non-stationarity. Temporarily reduce position size or pause trading until half-life stabilizes. Recalculate half-life estimates quarterly using rolling windows to detect trends. If half-life persistently increases above forty-five days, consider retiring the pair from your trading system. If half-life shortens dramatically, verify increased stationarity through Augmented Dickey-Fuller retesting before expanding position sizes. Dynamic half-life monitoring prevents capital losses from trading deteriorating relationships.
Common Misconceptions About Half-Life Mean Reversion
A long half-life in a cryptocurrency pair means the mean reversion relationship is stronger and more profitable.
Long half-life indicates slower reversion, not stronger relationships. A twenty-day half-life is actually weaker than a five-day half-life because price deviations take longer to correct. Longer half-lives increase capital duration risk, reduce annual position turnover, and extend trader exposure to regime changes. Most successful crypto pairs traders actively avoid long half-life pairs, preferring shorter half-life relationships. The strength misconception confuses reversion persistence with reversion speed—profitable trading demands fast reversion, not persistent correlations.
If I calculate half-life once when I discover a good trading pair, I can rely on that figure for years of trading.
Market regimes shift constantly, especially in crypto markets where correlations change rapidly. Half-life values are time-dependent estimates that degrade as market conditions evolve. A pair with stable five-day half-life can deteriorate to twenty-day half-life within months as market structure changes. Professional traders recalculate half-life quarterly at minimum and monitor half-life trends continuously. Trading with stale half-life estimates exposes you to unknown mean-reversion characteristics and suboptimal position sizing.
Half-life and correlation are the same metric for evaluating cryptocurrency pair quality.
Correlation measures relationship strength between two assets; half-life measures reversion speed of that relationship. Two highly correlated assets might have very long half-lives (weak mean reversion) or short half-lives (strong mean reversion). You need both metrics: correlation confirms relationships exist, while half-life determines trade feasibility. High correlation without short half-life creates false trading signals and capital drain. Evaluate pairs by combining correlation strength, stationarity confirmation, and half-life shortness for comprehensive pair assessment.