7-3 Estimating a Population Standard Deviation or Variance 349 4. To get a confidence interval estimate of s, take the square root of each component of the above confidence interval. 5. Round the confidence interval limits using the round-off rule given in the preceding Key Elements box. Using Confidence Intervals for Comparisons or Hypothesis Tests Comparisons Confidence intervals can be used informally to compare the variation in different data sets, but the overlapping of confidence intervals should not be used for making formal and final conclusions about equality of variances or standard deviations. continued EXAMPLE 2 Confidence Interval Estimate of S for Pulse Rates Listed below is a simple random sample of pulse rates (beats per minute or bpm) obtained from adult females (based on Data Set 1 “Body Data” in Appendix B). Construct a 95% confidence interval estimate of s. 76 76 86 74 66 62 78 68 62 62 74 80 54 74 74 84 60 52 84 66 56 66 SOLUTION REQUIREMENT CHECK Step 1: Check requirements. (1) The sample is a simple random sample. (2) The accompanying normal quantile plot suggests that the sample is from a normally distributed population (because the points are close to a straight-line pattern). Step 2: Using Technology The confidence interval can be found using technology. The Statdisk display shows the confidence interval estimates of the population standard deviation s and the population variance s 2. Rounding the confidence interval limits to one decimal place, we get this 95% confidence interval estimate of s:7.6 bpm 6 s 6 14.2 bpm. Statdisk Go Figure 1 minute and 41 seconds: The mean time it takes to talk to a human customer service representative when calling an 800 number at one of the top 100 Internet retailers.
RkJQdWJsaXNoZXIy NjM5ODQ=