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A study was conducted to measure the effectiveness of hypnotism in reducing pain. The measurements are centimeters on a pain scale before and after hypnosis. Assume that the paired sample data are simple random samples and that the differences have a distribution that is approximately normal. Does hypnotism appear to be effective in reducing pain? Before 6.3 4.0 9.2 9.3 11.3 8.6 8.3 5.2 After 6.5 2.5 7.7 8.4 8.6 6.1 3.9 2.8 In this example, ud is the mean value of the differences d for the population of all pairs of data, where each individual difference d is defined as the difference in the measurements on a pain scale before and after hypnosis. What is the test statistic for this hypothesis test