Find the sample size needed to give, with 95% confidence, a margin of error within ±3% when estimating a proportion. First, find the sample size needed if we have no prior knowledge about the population proportion p. Then find the sample size needed if we have reason to believe that p ≈ 0.7. Finally, find the sample size needed if we assume p ≈ 0.9. Comment on the relationship between the sample size and estimates of p.

We examine the effect of different inputs on determining the sample size needed to obtain a specific margin of error when finding a confidence interval for a proportion.