Power Analysis Calculator — 公式
## How to Perform a Power Analysis
### Formula
**n per group = ((z_alpha/2 + z_beta) / d)^2**
Power is the probability of correctly rejecting a false null hypothesis (detecting a real effect). This formula estimates the sample size needed per group for a two-sample test. Higher power, smaller effect sizes, and lower alpha all require larger samples.
### Formula
**n per group = ((z_alpha/2 + z_beta) / d)^2**
Power is the probability of correctly rejecting a false null hypothesis (detecting a real effect). This formula estimates the sample size needed per group for a two-sample test. Higher power, smaller effect sizes, and lower alpha all require larger samples.
计算示例
Detect a medium effect (d = 0.5) with 80% power at alpha = 0.05.
- n = ((1.96 + 0.842) / 0.5)^2
- = (2.802 / 0.5)^2
- = 5.604^2
- = 31.4
- Round up: 32 per group, 64 total