A political candidate has asked you to conduct a poll to determine what percentage of people support her. If the candidate only wants a 0.1% margin of error at a 99.5% confidence level, what size of sample is needed? ______
Solution :
Given that,
=
0.5
1 -
= 1 - 0.5 = 0.5
margin of error = E = 0.1% = 0.001
At 99.5% confidence level the z is
Z/2
= Z0.0025 = 2.81( Using z table )
Sample size = n = (Z/2
/ E)2 *
* (1 -
)
= (2.81 / 0.001)2 * 0.5 * 0.5
= 1974025
Sample size =1974025
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