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Sample size is the number of observations needed in a study to achieve a specified margin of error and confidence level. Larger samples give more precise estimates but cost more to collect. The required n depends on confidence level, expected proportion, and acceptable error.

Hướng dẫn từng bước

1. 1For proportions: n = z² × p(1-p) / E²
2. 2z = 1.96 for 95% confidence · z = 2.576 for 99% confidence
3. 3p = expected proportion (use 0.5 if unknown — gives maximum n)
4. 4E = desired margin of error as a decimal (e.g. 0.05 for ±5%)

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