Chapter 9, Problem 70SE

Shoveling is not exactly a high-tech activity, but it will continue to be a required task even in our information age. The article “A Shovel with a Perforated Blade Reduces Energy Expenditure Required for Digging Wet Clay” (Human Factors, 2010: 492–502) reported on an experiment in which 13 workers were each provided with both a conventional shovel and a shovel whose blade was perforated with small holes. The authors of the cited article provided the following data on stable energy expenditure [(kcal/kg(subject)/lb(clay)]:

Worker:	1	2	3	4
Conventional:	.0011	.0014	.0018	.0022
Perforated:	.0011	.0010	.0019	.0013
Worker:	5	6	7
Conventional	.0010	.0016	.0028
Perforated:	.0011	.0017	.0024
Worker:	8	9	10
Conventional:	.0020	.0015	.0014
Perforated:	.0020	.0013	.0013
Worker:	11	12	13
Conventional:	.0023	.0017	.0020
Perforated:	.0017	.0015	.0013

a. Calculate a confidence interval at the 95% confidence level for the true average difference between energy expenditure for the conventional shovel and the perforated shovel (the relevant normal probability plot shows a reasonably linear pattern). Based on this interval, does it appear that the shovels differ with respect to true average energy expenditure? Explain.

b. Carry out a test of hypotheses at significance level .05 to see if true average energy expenditure using the conventional shovel exceeds that using the perforated shovel.