18. a. A repeated-measures study with a sample of n = 16 participants produces a mean difference of Mp = 4 with a standard deviation of s = 8. Use a two-tailed hypothesis test with a = .05 to determine whether it is likely that this sample came from a population with up = 0. b. Now assume that the sample mean difference is Mp = 10, and once again visualize the sample distribution. Use a two-tailed hypothesis test with a = .05 to determine whether it is likely that this sample came from a population with up = 0. c. Explain how the size of the sample mean difference influences the likelihood of finding a significant mean difference