at influences the Sample Size? 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. Find the sample size needed to give a margin of error to estimate a proportion within + 4% with 99 % confidence. With 95 % confidence. With 90 % confidence. (Assume no prior knowledge about the population proportion p.) Round your answers up to the nearest integer. Confidence Sample Size 99 % : i 95 % : i 90 %