The Netherlands SubThalamic and Pallidal Stimulation (NSTAPS) study was initiated to test the hypothesis that bilateral globus pallidus deep brain stimulation would improve disability to a greater extent than would bilateral subthalamic nucleus deep brain stimulation. By contrast with previous studies that investigated the effectiveness of deep brain stimulation, we chose a generic disability scale as the primary outcome measure, which was weighted by time spent in either the on phase or the off phase. Our results did not show a between-group difference for this primary outcome. As stipulated in our discussion section and in line with Erwin Montgomery's remarks, this result could be explained by insufficient statistical power raising the probability of a type II error. We are of course aware that the absence of difference in our primary outcome does not imply equivalence of the two procedures. However, this idea was not our conclusion, nor was it the rationale of the accompanying Comment.
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