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

Where z_α/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 z_α/2 = 1.96 and d = 0.15 to get a sample size of n = 86. Find the sample size required to estimate the standard deviation of IQ scores of data scientists, assuming that we want 98% confidence that s is within 5% of s.

Table 7-2

n || 2 (20/12) d