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 1% margin of error at a 99% 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 = 1% = 0.01

At 99% confidence level the z is,

= 1 - 99%

= 1 - 0.99 = 0.01

/2 = 0.005

Z/2 = 2.58    ( Using z table )

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

= (2.58 / 0.01)2 * 0.5 * 0.5

=16641

Sample size = 16641