Sample size

The sample size calculation is based on the results of trials by Li et al. [18] and Ji et al. [19] and the recommendation of acupuncture specialists in China. The mean value of the NDI score in the 2.5 Hz group is 82.28, the standard deviation is 6.97; the mean value of the NDI score in the 2 Hz group is 86.73, the standard deviation is 7.10; the mean value of the NDI score in the 1 Hz group is 76.50, the standard deviation is 8.06; the mean value of the NDI score in the control group is 65.85, the standard deviation is 16.47. To detect a significant difference between any two groups with a power of 90% and a type I error of 5%, the calculated number of patients is 17. Considering a 30% dropout rate, the total sample size required is 88 patients.