Posted by Johniece McCoy on .
If you want to be 95% confident of estimating the population proportion to within a sampling error of and there is historical evidence that the population proportion is approximately 0.40, what sample size is needed?
Formula to find sample size:
n = [(z-value)^2 * p * q]/E^2
... where n = sample size, z-value is 1.96, p = .4, q = 1 - p, ^2 means squared, * means to multiply, and E = ? (missing in problem).
Plug values into the formula and calculate n.
I hope this will help get you started.