What Is Mean Reversion?
Mean reversion means trading against a move on the expectation that price returns toward its average. It rests on price changes being negatively correlated — a move up followed by a move down — which is the exact opposite of the premise trend following relies on, measured on the same series.
The other half of the pair. Everything the trend following page assumes, this one assumes the reverse of — on the same market, at the same moment.
How it works
Price strays from its average, so trade the return.
The edges are where you act and the middle is where you exit. That is the whole shape of it, and it needs a trading range to make any sense.
The premise, measured
Mean reversion bets that a move up is more likely to be followed by a move down. Negative autocorrelation — the same number the trend following page measures, with the opposite sign wanted.
On the range scene above it measured +0.041, standard error 0.158. Well inside one standard error of zero, on 40 observations. This chart supports neither strategy.
On the slow view of the shared history it measured −0.377 — the sign mean reversion wants, about two and a half standard errors from zero on 46 observations.
So the two strategies are not opinions about markets in general. They are opinions about a specific series at a specific resolution, and the same history gives a different answer at different speeds.
Which is the most useful thing on either page: before choosing between them, you can go and measure, and the answer is not the same everywhere.
Where it works
A range with edges you can name. Bollinger Bands or a distance from a moving average turn “stretched” into a number, which is the operational form of the idea.
And the target is the average, not the far edge. Taking the middle is a smaller win with a much higher chance of arriving, and stretching for the other side is how a working strategy becomes a losing one.
The shape of the returns
This is what makes it psychologically dangerous and it is worth being explicit.
Mean reversion produces many small wins and occasional large losses. The win rate is high, the account rises steadily, and the strategy feels correct for a long time.
Trend following is the mirror — many small losses and occasional large wins, which feels wrong almost all the time and is not.
Neither shape is better. But a high win rate is evidence of the shape, not of the edge, and the number that matters is what the losses cost when they come.
What makes a market revert
The measurement tells you whether a series reverted. It is worth asking why any market would.
Trend following has an easy story: information arrives gradually, people react at different speeds, and a move continues as the slower participants catch up.
Mean reversion’s story is about supply. A move that ran without new information has left people holding positions at prices they did not intend to pay, and some of them want out — which supplies selling into a rise that had no reason behind it.
That predicts something specific and checkable: reversion should be stronger where the move had no news behind it, and weaker where something actually changed. A market that gapped on an earnings release is a poor candidate; the same market drifting up on a quiet afternoon is a better one.
Which is the practical filter this strategy most often lacks. The band or the oscillator says “stretched” without asking why, and the why is exactly what separates a move that comes back from one that has repriced permanently.
A worked example
Establish the range from market structure first. No range, no trade — that is the whole filter.
Mark the edges from price, and only then look at a band or an oscillator for a second reason.
Enter against the move at the edge, target the middle.
And the stop goes beyond the edge, close enough that the strategy’s rare large loss is bounded. Trading this without a stop is the version that ends badly, because the losing case is exactly the one where price keeps going.
The original data
Across our study of 24,971 trading videos, 160 cover mean reversion. The median one gets 3,938 views, 92% never pass 50,000, and the median length is 11.0 minutes.
That 92% is among the highest saturations measured here, and the topic is far less popular than its opposite: trend following has 227 videos and momentum 106.
The corpus carries description text for only 3 of those 160, far too few to say anything about how the topic is written.
When it fails
Fading a trend
Every close above the early high was a signal by the rule, and the market kept going.
This is the specific failure and it is not symmetrical with trend following’s. A trend follower in a range loses a little repeatedly; a mean reverter in a trend loses a great deal once.
The win rate reassures you
Covered above. A run of small wins is what this strategy looks like when it is working and also when it is about to hurt you, and there is no way to tell the two apart from the equity curve.
There is no stop
The natural exit is “when price comes back”, which is not a price. A strategy whose losing case has no defined end is the one that ends an account, and it is a very easy mistake to make here because the winning case is so reliable.
You judged the edge before it broke
The top of a range and the start of a breakout are the same bar. Fading is correct in one case and catastrophic in the other, and this is the moment you have to choose.
Related
Trend following is the opposite bet, and neither page means much without the other.
Trading range is the condition this needs, read from price.
And Bollinger Bands is the usual way of putting a number on “stretched”.
The trap in this one is that it feels good. Most of the trades work, you get a lot of small wins, and the account grinds up in a way that is genuinely pleasant. Then one move does not come back and it takes more than the last twenty gave you. I am not against it, but I would say to anyone running it that the win rate is the least informative number in the whole strategy.
— Michael Whitman, from this video
This page is educational, not financial advice. Test every idea on your own charts before risking money.