Rehabilitation medicine researchers at the University of Washington investigated whether virtual-reality hypnosis can relieve pain in trauma patients (International Journal of Clinical and Experimental Hypnosis, Vol. 58, 2010). Study participants were 20 patients treated at a major Level 1 trauma center. The patients were randomly assigned to one of three treatment groups: (1) VRH-virtual-reality hypnosis with posthypnotic suggestions for pain reduction, (2) VRD-virtual-reality distraction from pain without hypnotic suggestions for pain reduction, and (3) Control-no virtual-reality hypnosis, but standard care. Pain intensity was measured (on a 100-point scale) prior to treatment and 1 hour after treatment. The differences in pain-intensity levels (before minus after) are listed in the accompanying table.

a. Conduct a nonparametric test to determine whether the distribution of differences in pain-intensity levels differs for the three treatments. Test using a = .05. What do you conclude?

b. Combine the patients in the VRD and Control groups into a single treatment group (called non-posthypnotic suggestion). Compare the VRH treatment patients with the patients in this new group using the appropriate nonparametric test (using a = .05). What do you conclude?

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VRH VRD Control -20 -56 -12 63 51 21 12 -7 29 -34 16 -14 -7 -44 43 -11