Estimate how many independent forecast-error observations are needed to measure a mean accuracy metric with a chosen margin of error. Enter an estimated standard deviation of the error metric, desired half-width, and confidence level. The normal-approximation result is useful for planning MAE, bias, or similar continuous-error evaluations when a pilot estimate of variability is available.
Base sample n = (zσ/E)², rounded upward, where σ is the forecast-error standard deviation and E is the desired confidence-interval half-width. Buffered sample = ceil[n/(1−buffer rate)].
The primary result is conditional on the values and statistical assumptions entered. Read the secondary results to understand uncertainty, workload, or design sensitivity before making a decision.
This planning estimate is not a substitute for a study protocol, domain review, or a method chosen for the final data distribution.
With an estimated standard deviation of 12 units, a 2-unit margin, and 95% confidence, the base requirement is ceil[(1.959964×12/2)²] = 139 usable observations.
The calculator uses a standard statistical approximation. Small samples, highly skewed outcomes, or model misspecification can make the estimate less accurate.
Yes. A 90% setting gives a narrower interval or lower sample requirement, while a 95% setting provides more conservative coverage.
Use zero only where the input allows it. A rate calculation still needs a positive total or a defined prior so that division by zero is avoided.
No. It summarizes uncertainty or planning assumptions; study design, randomization, measurement quality, and confounding still matter.
Keep rates and intervals at the shown precision, but round required counts upward because a fraction of a sample or processing unit is not usable.
| Item | How it is used |
|---|---|
| Observed or planned sample | Sets the available evidence or workload. |
| Uncertainty setting | Controls interval width or rejection threshold. |
| Variability or rate | Translates the sample into uncertainty, power, or capacity. |