Mean reversion vs. momentum: two families of trading rules

Strip away the jargon and most systematic trading rules are a variation on one of two opposite ideas about how prices behave.

The two families

• Momentum bets that what's been moving will keep moving — winners keep winning, at least for a while. The classic academic evidence comes from Jegadeesh and Titman's 1993 study showing that buying recent winners and selling recent losers earned abnormal returns over intermediate horizons.
• Mean reversion bets the opposite — that prices stretched far from some "normal" level tend to snap back. Sell what's overstretched, buy what's oversold.

Almost every rules-based strategy is, at heart, a flavor of one of these. Knowing which one you're trading clarifies what you're really betting on.

Why it matters

The crucial insight: each works in the environment the other fails in.

• Momentum thrives in trending markets and gets shredded in choppy, range-bound ones, where it keeps buying tops and selling bottoms.
• Mean reversion thrives in range-bound markets and gets destroyed in strong trends, where "it's overstretched, it'll snap back" becomes "it kept going and ran me over."

There is no free lunch. A strategy that prints money for a while may simply be matched to the current regime — and regimes change.

The discipline this demands

Because each family has an environment that punishes it, the dangerous move is to abandon a sound rule during its rough patch — usually right before it would have worked — and chase whatever's hot. That's recency bias wearing a strategy costume.

This is, again, an argument for pre-commitment: decide your rules and your risk limits in advance, understand the conditions where they'll struggle, and let consistency — not the last few weeks — carry you through. The edge, if there is one, lives in the discipline to keep applying the rule, not in switching families every time the weather turns.

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This article is educational and does not constitute investment advice or a recommendation. Options trading involves substantial risk and is not suitable for every investor. Autopilot Options does not guarantee profits or prevent losses. Past performance and historical data do not guarantee future results.