Overfitting: how do you know you've done it?

An overfitted strategy is tailored to the past: perfect on historical data, useless going forward. The tell-tale signs are too many rules, too many parameters and a backtest that's suspiciously smooth.

What's your overfitting checklist?

• the signs you look for in a backtest
• how you simplify a strategy that's too tuned
• the overfitted system you believed in once

The expectancy guide explains the difference between edge and coincidence.