Question
Asked Nov 16, 2019
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A political candidate has asked you to conduct a poll to determine what percentage of people support her. If the candidate only wants a 9% margin of error at a 90% confidence level, what size of sample is needed?

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Expert Answer

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Step 1

Given:

Margin of error (E) = 0.09

Confidence level = 90%

Since, the proportion of people that support her (p) is not given then it will be assumed as 0.5.

Step 2

The sample size could be calculated using the following formula:

n= p(1-p)
E
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n= p(1-p) E

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Step 3

The sample size at 90% confidence ...

The value of Z
corresponding to 90% confidence level is 1.645
n p(1-p)
E
1.645
=0.5(1-0.5)
0.09
=0.25x334.077
83.519
84
8
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The value of Z corresponding to 90% confidence level is 1.645 n p(1-p) E 1.645 =0.5(1-0.5) 0.09 =0.25x334.077 83.519 84 8

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