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In a 5-year follow-up of bilateral stimulation of the subthalamic nucleus among 49 patients with advanced Parkinson’s disease, investigators assessed changes in symptoms as measured by the Unified Parkinson’s Disease Rating Scale (
The above study had no control group. Assuming that the same standard deviation of change would occur among controls and the mean change among controls = 0, how many participants would be necessary to detect a mean difference of 5 units of change between those receiving stimulation and a control group of equal size with 80% power if a two-sided test is used with α = .05?
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