Question

What is needed to compute a sample size, n, to obtain a confidence interval with a specified margin of error, m?

Answer 1

If we want to estimate the sample size with no prior estimate of proportion, then confidence level and margin of error are enough to find the required sample size

n = 0.25*(z/m)^2

If we want to estimate the sample size with prior estimate of proportion, then confidence level and margin of error are not enough to find the required sample size because we need the proportion value p to find the required sample size

n = ((1-p)*p)*(z/m)^2

and

If we want to estimate the sample size for mean, then we need population standard deviation with confidence level and margin of error m

n = ((z*sd)/m)^2