2.2. Sample Size Calculation

We will investigate the therapeutic effects of Tai Chi for FC patients. According to our preliminary study from which we recruited 10 FC patients with the Tai Chi intervention, the mean improvement of weekly complete spontaneous bowel movements (CSBMs) of Tai Chi was 1.67 ± 0.89 times. A systematic review [12] focusing on the management of FC reported the mean improvement of weekly CSBMs of polyethylene glycol (the first-line medication of FC) was 1.8 times. We hypothesize that the therapeutic effects of Tai Chi are not less than the polyethylene glycol. Considering α = 0.05, 1 − β = 0.8, the study design required a sample size of 36 for each group with the one-sample noninferiority test [13], with a drop-out rate of 10%. A total of 40 patients with FC and 40 HS will be finally recruited.