6 PAF-study: results of a randomized controlled trial 151 a mean of 1.75 (μV) at rest, with a standard deviation of 1.75. Based on a slightly conservative standard deviation of 1.8, and a difference to be detected of 1.0 between the treatment group and the control group, we concluded that at least 70 patients in each treatment arm was required to detect a difference of 1.0 between the treatment group and the control group with postponed treatment. This sample size provided ample power (>90%) to detect a moderate effect size with a nominal alpha level of 5%. Randomization The surgeon and the principal investigator approached the patient and informed the patient about the study. Patients who met the eligibility criteria were randomly assigned to the PFPT treatment group or to the control group receiving postponed PFPT (1:1 allocation, random block sizes of 4,6 and 8). The randomization was computer generated using Castor EDC.34 A unique record number was generated, and the allocation was disclosed. The principal investigator was not able to access the randomization sequence and had a decoding list with randomization numbers and patient identification numbers in the investigator site file. Only the coordinating surgeon and principal investigator had access to the key to the code. The principal investigator informed the patient about group allocation and follow-up appointments. Blinding The principal investigator, who was also involved in the data analysis was not blinded for allocation. Because of the nature of the intervention, the principal investigator, collaborating pelvic floor physical therapists and patients could not be blinded. However, the surgeon performing the 8- and 20-week follow-up to investigate the healing of the fissure, resting anal sphincter pressure and pelvic floor dyssynergia was blinded to group allocation. Statistical analysis Data were analysed using Statistical Packages for Social Sciences (SPSS, Chicago, II, USA, version 26.0). Descriptive methods were used to assess quality of data, homogeneity of treatment groups and endpoints. Normality of the data were analysed with histograms. Data are presented using mean (SD), median (min-max) for the
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