Sample size calculation
®, PCOS
Prior to this RCT, we conducted a short pilot trial with 30 women with PCOS (EC number 30–205 ex 17/18), randomly assigning 10 women into three probiotic intervention arms respectively, both to test our methodology as well as to assess the feasibility of improving PCOS symptoms with probiotics (Borzan V., Sommer F., Riedl, R., Obermayer-Pietsch B., 2020, data on file).In the pilot study 10 participants received OMNi-BiOTiC® metabolic for 3 months and showed a median (minimum-maximum) reduction in free testosterone levels of -0.3 pg/ml (-1.7-2.5). We assumed that over 6 months the reduction in the probiotic group would be improved to -0.6 pg/ml, which corresponds to 20% of the free testosterone levels found in healthy women based on the cut-off value of 3,16 pg/ml free testosterone in our Endocrinology Lab platform. A sample size of 54 in each group would have 80% power to detect a difference in means of -0.6 pg/ml assuming that the common standard deviation was 1.1 pg/ml using a two group t-test with a 5% two-sided significance level. Including a 10% dropout, 60 participants per group had to be included. For the metformin group in the open part of the trial, 60 participants were recruited as well. Therefore, the total anticipated sample size was 180.