24. Low-back pain (LBP) is a serious health problem in many industrial settings. The article Isodynamic Evaluation of Trunk Muscles and Low-Back Pain Among Workers in a Steel Factory (Ergonomics, 1995: 2107—2117) reported the accompanying summary data on lateral range of motion (degrees) for a sample of workers without a history of LBP and another sample with a history of this malady.

Sample Sample Sample Condition Size Mean SD No LBP 28 91.5 5.5 LBP 31 88.3 7.8 Calculate a 90% con dence interval for the difference between population mean extent of lateral motion for the two conditions. Does the interval suggest that population mean lateral motion differs for the two conditions? Is the message different if we use a con dence level of 95%?