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Sample Size Formulas
Here are the formulas used in our Sample Size Calculator:
Sample Size
| ss = | Z2 * (p) * (1-p) | |
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| c2 |
where:
| Z = Z value (e.g. 1.96 for 95% confidence level) p = percentage picking a choice, expressed as decimal (.5 used for sample size needed) c = confidence interval, expressed as decimal (e.g., .04 = ±4) |
Correction for Finite Population
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ss |
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| new ss = |
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where:
| pop = population |
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