10.147 Some 20 million Americans visit chiropractors annually, and the number of practitioners in the United States is 55,000, nearly double the number two decades ago, according to the American Chiropractic Association. The New England Journal of Medicine released a report showing the results of a study that compared chiropractic spinal manipulation (CSM) with physical therapy for treatment of acute lower back pain. After 2 years of treatment, CSM was found to be no more effective at either reducing missed work or preventing a relapse.

Suppose a similar study of 60 patients is made by dividing the sample into two groups. For 1 year, one group is given CSM and the other, physical therapy. During the 1-year period, the number of missed days at work as a result of lower back pain is measured:

Group n Mean Std. Dev.

CSM (1) 32 10.6 4.8 Therapy (2) 28 12.5 6.3 Do these results show that the mean number of missed days of work for people suffering from acute back pain is significantly less for those receiving CSM than for those undergoing physical therapy? Assume normality and use a 0.01 level of significance.

a. Solve using the p-value approach.

b. Solve using the classical approach.