Your 100-trade sample knows less than you think
You have run a system 100 times. Expectancy is +0.31R. It feels established.
It is not. That figure is a single sample from a distribution, and the range of true values consistent with it is far wider than most traders assume.
Understanding how wide is what separates someone who trades a system from someone who *manages* one.
The confidence interval nobody calculates
The standard error of your expectancy estimate is roughly:
`` SE ≈ standard deviation of trade results ÷ √(number of trades) ``
For a typical system with a per-trade standard deviation of about 1.5R:
| Trades | Standard error | 95% range around +0.31R |
|---|---|---|
| 50 | 0.21R | −0.10 to +0.72 |
| 100 | 0.15R | +0.01 to +0.61 |
| 300 | 0.087R | +0.14 to +0.48 |