Question

4. A political candidate has asked you to conduct a poll to determine what percentage of people support her. If the candidate only wants a 2% margin of error at a 90% confidence level, what size of sample is needed? Give your answer in whole people.

Answer 1

SOLUTION

Given that,

= 0.5

1 - = 1 - 0.5 = 0.5

margin of error = E = 2% = 0.02

At 90% confidence level the z is ,

= 1 - 90% = 1 - 0.90 = 0.10

/ 2 = 0.10 / 2 = 0.05

Z_/2 = Z_0.05 = 1.645

Sample size = n = (Z_/2 / E)² * * (1 - )

= (1.645 * 0.02)² * 0.5 * 0.5

= 1691.2656

Sample size = 1692