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Sample Size Calculator — Proportion, Mean, FPC & Response Rate

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Planning for Confidence level Margin of error (percentage points) Enter 5 for ±5 percentage points.Expected proportion (%) Use 50 when no prior estimate is available for the conservative basic formula.Finite population size (0 = very large) Design effect Use 1 for a simple-random-sample planning model.Expected response rate (%) Used only to estimate how many invitations may be needed.

Calculated result

385 completed responses

Infinite-population raw n₀: 384.16

Finite-population correction not applied

After design effect 1: 384.16

Invitations at 100% response rate: 385

Show the working

1. Base calculation: 1.96² × 0.5 × 0.5 ÷ 0.05² = 384.16.
2. Treat population as large/unspecified, so n = n₀.
3. Multiply by design effect 1 and round up → 385.
4. Invitation planning = ceil(385 ÷ 1) = 385.

This is planning arithmetic for the selected simple formulas. Complex survey designs, power calculations, clustering, weighting and nonresponse bias can require specialist methods.

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