Calculate statistical power for a given effect size and sample size.
Required sample size scales with the inverse square of effect size, so detecting a half-size effect needs four times the participants. Eighty per cent power is the conventional minimum. Underpowered studies waste resources and produce unreliable literature, because the significant results that do emerge are disproportionately overestimates.
Power Analysis
Power = P(reject H₀ | H₁ true); required n per group ≈ 2(z_α + z_β)² ÷ d²
Power = P(reject H₀ | H₁ true); required n per group ≈ 2(z_α + z_β)² ÷ d² Required sample size scales with the inverse square of effect size, so detecting a half-size effect needs four times the participants. Eighty per cent power is the conventional minimum.
Underpowered studies waste resources and produce unreliable literature, because the significant results that do emerge are disproportionately overestimates.
This calculator takes 3 inputs: Effect size, Sample size per group, Significance level. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.