Here is the design of a clinical trial:

Official Title: Open-Label Placebo Treatment of Women With Premenstrual Syndrome: A Randomized Controlled Trial

Included conditions:
- Premenstrual Syndrome

Study Armgroups:
- {'label': 'Treatment as Usual', 'type': 'NO_INTERVENTION', 'description': 'The treatment as usual (TAU) group will control for regression to the mean, spontaneous remission, natural course of disease, and the participants-provider interaction. Participants of the TAU group are allowed to continue their usual medication intake, given they are already on a stable dose (at least 30 days of intake) and the medication is not listed in the exclusion criteria.'}
- {'label': 'Integrative Open-Label Placebo', 'type': 'ACTIVE_COMPARATOR', 'description': 'The intervention will encompass an integrative administration of "P-Dragees rosa Lichtenstein", which are pink placebo dragées without any active ingredient. Each dragée contents the following substances: lactose monohydrate; magnesium stearate (Ph. Eur.); microcrystalline cellulose; highly dispersed silicon dioxide; white clay, macrogol glycerolhydroxy stearate (Ph. Eur.); Arabic gum; montanglycol wax; povidone (K 25); talcum; titanium dioxide (E 171); erythrosine; aluminium salt (E 127); calcium carbonate; sucrose; glucose syrup; maize starch; macrogol 6000.\n\nAll participants will be informed that the administered dragées are placebo dragées and participants will be instructed to take two dragées a day for six weeks. (Amendment regarding dosage since 08/18)', 'interventionNames': ['Other: P-Dragees rosa Lichtenstein']}
- {'label': 'Open-Label Placebo', 'type': 'ACTIVE_COMPARATOR', 'description': 'The intervention will encompass an administration of "P-Dragees rosa Lichtenstein", which are pink placebo dragées without any active ingredient. Each dragée contents the following substances: lactose monohydrate; magnesium stearate (Ph. Eur.); microcrystalline cellulose; highly dispersed silicon dioxide; white clay, macrogol glycerolhydroxy stearate (Ph. Eur.); Arabic gum; montanglycol wax; povidone (K 25); talcum; titanium dioxide (E 171); erythrosine; aluminium salt (E 127); calcium carbonate; sucrose; glucose syrup; maize starch; macrogol 6000.\n\nAll participants will be informed that the administered dragées are placebo dragées and participants will be instructed to take two dragées a day for six weeks. (Amendment regarding dosage since 08/18)', 'interventionNames': ['Other: P-Dragees rosa Lichtenstein']}

Interventions:
- {'type': 'OTHER', 'name': 'P-Dragees rosa Lichtenstein', 'description': 'Placebo dragées', 'armGroupLabels': ['Integrative Open-Label Placebo', 'Open-Label Placebo']}

Primary Outcomes:
- {'measure': 'PMS symptom intensity assessed by a PMS symptom diary sub sum score', 'description': 'Symptom intensity will be assessed by an intensity sub scale of the PMS symptom diary. Intensity will be rated by means of a six-level Likert scale, whereat 1 is the lowest rating of symptom intensity and 6 the highest.', 'timeFrame': 'Continuous measurement, starting from day 1 of the menstrual cycle (length of each cycle is on average 28 days) until the individual last day of the third menstrual cycle of each participant (assessment across three menstrual cycles in total)'}
- {'measure': 'PMS symptom interference assessed by a PMS symptom diary sub sum score', 'description': 'Symptom interference will be assessed by an interference sub scale of the PMS symptom diary. Interference will be rated by means of a six-level Likert scale, whereat 1 is the lowest rating of interference and 6 the highest.', 'timeFrame': 'Continuous measurement, starting from day 1 of the menstrual cycle (length of each cycle is on average 28 days) until the individual last day of the third menstrual cycle of each participant (assessment across three menstrual cycles in total)'}

Please estimate the sample size based on the assumption: 
Significance level (alpha) is set at 0.05. Power is considered at 0.8 and 0.9. A multilevel approach is adopted for more precise estimations. Correlation among different time points is assumed to be 0.5.
Sample size
        A calculation with a power analysis on the basis of an F-test and an analysis of covariance for three groups, using the statistical software G*Power, indicated a total sample size of 206 participants needed for a power of 0.9 and a total sample size of 158 participants for a power of 0.8 to detect a medium effect size of f=0.25 (equals d=0.5) with an alpha-level of 0.05.
        Since we will adopt a multilevel approach which enables more precise estimations, we also conducted a power analysis on a repeated-measures analysis of variance, using G*Power, whereby we are interested in the interaction between time (menstrual cycles, 3 levels) and study groups (3 levels). If the correlation for the outcome among the different time points (1â3 cycles) is assumed to be 0.5, then based on an alpha-level of 0.05, a power of 0.8 and a medium effect size of f=0.25, the required samples size is 36 (12 per group). Accordingly, for the main effect of menstrual cycle, we would need 30 participants (10 per group), and for the main effect of study group we would need 108 participants (36 per group). On this basis, we chose a conservative total sample size of 150 participants (50 per group). It is worth noting that most OLP studies reported effect sizes that are generally higher than d=0.5 (eg, chronic low back pain: d=0.771; irritable bowel syndrome: d=0.79).2 However, in another OLP study for patients suffering from major depressive disorder,5 the authors reported an effect size of d=0.54 while stating that the study was limited by low statistical power (ie, the findings did not support the hypothesis that OLPs are effective in depression). Since PMS is not only characterised by physical complaints, yet also by psychological symptoms such as depressive mood, and since there is no specific research on OLP effects and effect sizes in PMS, we considered a conservative medium effect size as more appropriate. This resulted in a more conservative sample size.