Figure 1From: The Felix-trial. Double-blind randomization of interspinous implant or bony decompression for treatment of spinal stenosis related intermittent neurogenic claudication Sample Size. N1: number of patients needed in the IPD group, P1: the chosen succes rate of the IPD group; P2: the succes rate of the decompression group (0.64); N2: number of patients needed in the decompression group (equal to N1); A: the alfa is two sided 0.05.Back to article page