What sample size gives 80% statistical power?

For two-sample t-test with medium effect (d=0.5), alpha=0.05, power=0.80: n=64 per group. For small effect (d=0.2): n=394 per group. For large effect (d=0.8): n=26 per group. Rule of thumb: power increases with sample size, effect size, and alpha level. Power = 1 - Type II error rate.

What is an adequate statistical power for experiments?

Standard power = 0.80 (80% chance of detecting a true effect). High-stakes experiments (medical, policy): power = 0.90-0.95. Industry standard for A/B testing: 0.80. Underpowered tests (power < 0.60) frequently report false negatives, leading teams to abandon effective changes.

Sample Size for Statistical Power Calculator

Calculate required sample size for desired statistical power given effect size, alpha level, and test type. Supports t-tests, proportions, and ANOVA.

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How to Use

Enter the values for the scenario you are assessing. Calculate required sample size for desired statistical power given effect size, alpha level, and test type. Supports t-tests, proportions, and ANOVA. Use the sample size for power result to inform your calculation.

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Sample Size for Statistical Power Calculator

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Frequently Asked Questions

What sample size gives 80% statistical power?

What is an adequate statistical power for experiments?