Sample Size for a Proportion
Plan binary-trial sample size using expected proportion and margin.
Your numbers
Required sample size
Normal approximation; 50% is conservative when the proportion is unknown. Cluster sampling needs a separate design adjustment.
Scenario comparison
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Formula
n₀=z²p(1−p)/E²; optionally apply finite-population correction.
Plan binary-trial sample size using expected proportion and margin.
Worked example
- Expected proportion (%)
- 50
- Desired margin (percentage points)
- 5
- Confidence level (%)
- 95
- Finite population, zero for unlimited
- 0
- Required sample size
- 385
Scope and limitations
Normal approximation; 50% is conservative when the proportion is unknown. Cluster sampling needs a separate design adjustment.
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Formula version: ef2c3376ca92 · Example checked: