Finding Sample Size Instead of using Table 7-2 for determining the sample size required to estimate a population standard deviation σ , the following formula can be used where zα/2 corresponds to the...

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

where zα/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 σ , 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 σ  , assuming that we want 98% confidence that s is within 15% of σ