(p. 339). Recall that 31 full-time office workers were seated for one hour at their desk or workstation, and the percentage of time their upper body stayed in a neutral position was measured. These measurements were made for both the head and the neck of each worker. A layout of the data is shown below, followed by summary statistics for all 31 workers. Suppose you want to compare the mean neutral percentage for the head to the mean neutral percentage for the neck. Layout of the data: Worker Head % Neck % 1 45 42 2 51 47 f 31 48 40 Summary Statistics: Sample mean Sample standard deviation Head 48.97% 22.13% Neck 43.20% 21.41% Source: Jun, D. et al. “Are measures of postural behavior using motion sensors in seated office workers reliable?,” Human Factors, Vol. 61, No. 7, November 2019 (Table 1).

a. Give the appropriate null and alternative hypotheses.

b. How should the data be analyzed, as an independent samples test or as a paired difference test? Explain.

c. Why are the summary statistics in the table insufficient to make the comparison?

d. Assume the differences between the head and neck measurements are calculated for each worker and that the mean of these differences is 5.77% and the standard deviation of these differences is 1.5%. Use this information to construct a 90% confidence interval for the difference between the mean neutral percentages of head and neck. What inference can you make? M08_MCCL3396_14_GE_C08.indd 479 25/09/2021 21:43 480 CHAPTER 8 ● Inferences Based on Two Samples

e. Interpret the interval, part

d. Can the geologists conclude that there is no evidence of a difference in the true THM means of all original holes and their twin holes drilled at the mine? Location 1st Hole 2nd Hole 1