90 Sample Size from Margin of Error
The margin of-error term in the confidence interval for one proportion can be solved for n. If we assume 95% confidence, use a z-value of 2, and assume the largest possible standard error to get a conservative answer, the formula simplifies to
N =(1/m2)
The resulting value for n is the approximate sample size required to get a margin of error of m, assuming the confidence level is 95%. The margin of error must be entered as a decimal, so a margin of error of 2 percentage points is entered as 0.02.
Ratio of Sample Sizes Find the sample size required for a margin of error of 3 percentage points, and then find one for a margin of error of 1.5 percentage points; for both, use a 95% confidence level.
Find the ratio of the larger sample size to the smaller sample size. To reduce the margin of error to half, by what do you need to multiply the sample size?