How do you determine sample size when the standard deviation

How do you determine sample size when the standard deviation, mean and confidence interval are provided?

Solution

You can use the formula

n = (z s / E)^2

where

n = the sample size

z = the critical z score for the confidence level (ex. z = 1.96 for 95% confidence)

s = the standard deviation

E = margin of error = (upper bound - lower bound) / 2