Here is the design of a clinical trial:

Official Title: Efficacy and Safety of Twice Daily TMBCZG in Mild to Moderate Vascular Dementia: Randomized, Double Blind, Parallel Group, Placebo Controlled, Multicenter Trial

Included conditions:
- Vascular Dementia

Study Armgroups:
- {'label': 'Placebo', 'type': 'PLACEBO_COMPARATOR', 'description': 'placebo identified to TMBCZG,0.1g per pill which contains 0mg TMBCZG，3 pills per time, 2 times per day for 24 weeks.', 'interventionNames': ['Other: placebo']}
- {'label': 'TMBCZG-high dose', 'type': 'EXPERIMENTAL', 'description': 'TMBCZG, 0.1g per pill which contains 14mg TMBCZG, 3 pills per time, 2 times per day for 24 weeks.', 'interventionNames': ['Drug: TMBCZG']}
- {'label': 'TMBCZG-medium dose', 'type': 'EXPERIMENTAL', 'description': 'TMBCZG( 0.1g per pill which contains 14mg TMBCZG) and placebo identified to TMBCZG(0.1g per pill which contains 0mg TMBCZG), 2 TMBCZG pills and 1 placebo pill per time, 2 times per day for 24 weeks.', 'interventionNames': ['Drug: TMBCZG', 'Other: placebo']}
- {'label': 'TMBCZG-low dose', 'type': 'EXPERIMENTAL', 'description': 'TMBCZG( 0.1g per pill which contains 14mg TMBCZG) and placebo identified to TMBCZG(0.1g per pill which contains 0mg TMBCZG), 1 TMBCZG pills and 2 placebo pill per time, 2 times per day for 24 weeks.', 'interventionNames': ['Drug: TMBCZG', 'Other: placebo']}

Interventions:
- {'type': 'DRUG', 'name': 'TMBCZG', 'description': '0.1g per pill which contains 14mg TMBCZG', 'armGroupLabels': ['TMBCZG-high dose', 'TMBCZG-low dose', 'TMBCZG-medium dose'], 'otherNames': ['TianMaBianChunZhiGanPian', 'TianMaYouJiDuoSuanBianZhiGanPian(TMYJDSBZG)']}
- {'type': 'OTHER', 'name': 'placebo', 'description': '0.1g per pill which contains 0mg TMBCZG', 'armGroupLabels': ['Placebo', 'TMBCZG-low dose', 'TMBCZG-medium dose']}

Primary Outcomes:
- {'measure': 'Vascular Dementia Assessment Scale-cognitive subscale(VADAS-Cog)', 'description': 'Change from baseline to end of double-blind treatment of VADAS-Cog.', 'timeFrame': 'baseline, 4-week, 12-week, 24-week and 28-week.'}
- {'measure': 'Clinical Dementia Rating-Sum of Boxes (CDR-SB)', 'description': 'Change from baseline to end of double-blind treatment of CDR-SB.', 'timeFrame': 'baseline, 4-week, 12-week, 24-week and 28-week.'}

Please estimate the sample size based on the assumption: 
The variance of the 4 groups of VADAS-cog means is 1.14, and the standard deviation within is 7.44 points. The 2-sided test level α = 0.20 and the power 1-β = 0.50. A greater rate of discontinuation of 20% is considered.
2.7
        Sample size
        There are no similar studies using TMBCZG tablets to treatment patients with VaD for the proposed study duration (24 weeks). The sample size was calculated based on the primary endpoints, VADAS-cog. It is hypothesized that the efficacy of TMBCZG in the treatment of mild to moderate VaD is similar to that of donepezil. Previous studies reported that the mean changes of ADAS-cog scores after 5 and 10âmg donepezil treatment were (5.75âÂ±â7.44) points and (2.25âÂ±â7.44) points, respectively. We assume that the placebo control group has a certain progression after 24 weeksâ treatment (â³â=ââ0.25). The mean scores of the 3 groups of VADAS-cog scale improvement were set at equal intervals, that is, the changes before and after the scores of each group were â0.25, 0.75, 1.50, 2.25, and the variance of the 4 groups of VADAS-cog means 1.14. The standard deviation within is 7.44 points. For this phase IIa study, the 2-sided test level Î± = 0.20 and the power 1-Î² = 0.50. This clinical trial adopts a balanced design and uses nQuery Advisor 7.0 to calculate, 32 cases are needed for each group. Considering a greater rate of discontinuation of 20%, the sample size was increased to 39 per group to ensure adequate patients to complete the study. The total number of cases was 160 cases, that is, 40 cases in the placebo control group and 40 cases in the 3 dose groups of the TMBCZG tablets. Note also that because this study is a pilot efficacy study (phase IIa), a larger sample size to reach a higher degree of statistical power is not required.