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Sample Size Formulas for our Sample Size Calculator

Here are the formulas used in our Sample Size Calculator:

Sample Size

ss = Z 2 * (p) * (1-p)
c 2

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

ss

new ss =
1+ ss-1

pop


Where: pop = population

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