http://en.wikipedia.org/wiki/Autocorrelation
Autocorrelation of returns is correlation(return[1...t-1],return[2...t]), or in other words the correlation between a series of returns and the same series of returns shifted one period forward or backward. Returns can be per-minute, per-day, or per-trade. It is a simple test to answer the questions:
Do returns come in streaks?
Do they oscillate?
Is there no pattern at all (random walk)?
It is particularly interesting to calculate autocorrelation across different time scales, and across the design space of a system. Why? Strong autocorrelating systems on short time scales naturally perform better with stops. So instead of brute force or real money testing different forms of stop losses, profit targets, trailing stops, or MA smoothing rules, look for the root cause of stop loss success⦠AUTOCORRELATION!
Even if a systemâs long-term net profitability is zero or negative, a strong positive (trending returns) or negative (oscillatory returns) autocorrelation on certain time scales can be taken advantage of in a system-of-systems design. Methods include activation/deactivation rules, regression, ranking/screens, or trend following rules.
A system with autocorrelation close to zero, even if nicely profitable will have volatile returns and will be more dangerous and psychologically painful to trade. You wonât know the system is dead until youâve taken on significant losses⦠when it effectively becomes strongly autocorrelating. Better to trade a strong autocorrelating system-of-system design that will automatically kill a dying system for you before losses accumulate.