Question

Any ideas please?
Simple random sample of voters will be taken in a large state. Researchers will construct an approximate 95% confidence interval for the percent of the state¢s voters who will vote for Candidate A. Find the minimum sample size needed to ensure that the width of the interval (right end minus left end) is at most 6%.

Thank you.

Answer 1

For a 95% confidence interval, 95% of the sample lie within (μ - 1.96
σ/√n) and (μ + 1.96 σ/√n).

Thus the width of the interval is: 3.92 σ/√n

So we need to find: n = (3.92 σ/ 6%)²

To do this we need to know (or estimate) the standard deviation (σ).