What is sample size?

What it means

Thirty trades is enough to notice a very large effect and nothing else. A hundred begins to be informative. Several hundred is where win rate and profit factor stabilise sufficiently to be treated as estimates rather than anecdotes.

Why it matters

This is a genuine and unavoidable problem for low-frequency strategies. A system taking ten trades a month generates 120 a year, so demonstrating an edge with reasonable confidence takes years, not months. Nothing can compress that timeline — running the same period through more backtests does not create more independent observations.

What this changes in practice

It is why our own figures carry the sample alongside them and why we say plainly that roughly ten trades a month makes any percentage unreliable. A vendor quoting a precise win rate from a few weeks of live trading is either unaware of this or relying on the reader being unaware.