Profit factor vs expectancy: which one to trust?

[Shadow Trader]

Profit factor is gross profit divided by gross loss. A value of 1.5 means 1.5 dollars won for every dollar lost. It's popular because it's easy to read and appears on most platform reports.

Expectancy tells the average result per trade. Both are useful, but they answer different questions, and each hides something.

Profit factor ignores trade count. A profit factor of 2.0 from 12 trades means almost nothing, while 1.3 from 3,000 trades means a lot. It also ignores how the profit is distributed, so a single huge winner can inflate the figure.

Expectancy per trade, with its confidence interval, makes the sample size explicit. It also translates directly into how much can be earned per trade and, with trade frequency, per week.

The sensible habit is reporting both, plus the number of trades and the maximum drawdown. A strategy that shows decent numbers across all four deserves attention.

A worked contrast: Strategy A has a profit factor of 1.8 over 40 trades. Strategy B has 1.25 over 2,500 trades. Most people prefer A at a glance. Most statisticians prefer B, because the sample is big enough to trust.

Which metrics get checked first when evaluating a strategy, and which one has been the most misleading in the past?