Barbara S.

asked • 04/28/20

margin of error formula to solve for n with 3% ME and 95%CI 1.96

Barbara S.

A candidate is planning a poll and wants to estimate voter support within 3% with 95% confidence. How large a sample does she need.
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04/28/20

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David L. answered • 04/28/20

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The equation to calculate n from the margin of error when the population proportion is unknown, we use

n = z2 * (0.25) / m2


In this scenario

z = 1.96 (for a 95% confidence percentage)

m = 0.03 (3%)


n = 1.962 * 0.25 / 0.032

= 1067.11


Since we can't have a fraction of a sample, we round up to the nearest whole integer n = 1068

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