Enter the acceptable margin of error, confidence level and population standard deviation to estimate the minimum sample size for a mean, planning sample counts with sufficient precision.
结果向上取整。
| Item | Formula / Note | Source / Standard |
|---|---|---|
| Sample size for a mean | n = ( z · sigma / E )^2, where E is the allowable error | Cochran WG, Sampling Techniques (3rd ed., 1977), Wiley |
| Finite population correction | n_adj = n / (1 + (n - 1)/N), where N is the population size | Cochran WG, Sampling Techniques (3rd ed., 1977) |
| Estimating sigma | Use a pilot sample SD s, or estimate sigma ≈ R / d2 from the range | Montgomery DC, Introduction to Statistical Quality Control (7th ed.) |
| Error vs. sample size | Halving the error quadruples the required sample size (inverse-square) | Cochran WG, Sampling Techniques (3rd ed., 1977) |