NIST’s proportion-interval method shows why twelve wins and twelve hundred wins provide different precision, even at the same observed rate.

What the source establishes

NIST describes Wilson confidence intervals for a binomial proportion and discusses why a simple symmetric approximation can be unsuitable, especially for small samples or extreme proportions. The method uses the observed count as well as the sample size. NIST/SEMATECH — confidence intervals for proportions ↗

Using that formula with z = 1.96, an illustrative 12 wins from 20 trials gives a 95% interval of approximately 38.7% to 78.1%. For 1,200 wins from 2,000 trials, the corresponding interval is approximately 57.8% to 62.1%. Both observed rates are 60%; neither dataset is claimed as real trading performance.

What the distinction changes

A percentage without its denominator conceals how much information produced it. The wider interval in the small example is a warning against turning a short winning history into a precise success-probability claim.

An interval also does not certify the dataset. Selective reporting, dependent observations and changing conditions can undermine the model before the formula is applied. Statistical precision and evidence quality need separate reviews.

Questions for the next review

Obtain the full trial count, inclusion rules and dated outcomes. Record the method and its assumptions alongside any interval. A frequentist 95% confidence level describes repeated-sample coverage of the procedure; it is not a promise about the next trade or a guarantee of profit.