Question

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? ______

Answer 1

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