Proportion Sample Size
Estimate survey sample size for a single proportion.
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Estimate the required sample size to measure a single proportion within a specified margin of error, with optional finite-population correction.
How it works
Method: n₀ = z² × p(1 − p)/e², where e is the margin of error as a proportion. Optional finite population correction: n = n₀/[1 + (n₀ − 1)/N].
Example: At 95% confidence with 5% margin and a 50% expected proportion, a large population requires 385 observations; with N = 1,000, the estimate is 278.
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