Finding Sample Size Instead of using Table 7-2 for determining the sample size required to estimate a population standard deviation s, the following formula can be used:

where za>2 corresponds to the confidence level and d is the decimal form of the percentage error. For example, to be 95% confident that s is within 15% of the value of s, use za>2 = 1.96 and d = 0.15 to get a sample size of n = 86.

Find the sample size required to estimate s, assuming that we want 98% confidence that s is within 15% of s.

n 12a/2 2d 2