Here is the design of a clinical trial:

Official Title: The Dutch Parkinson and Cognition Study (DUPARC): A Prospective Study on Cognitive Pathology in de Novo Parkinson'Disease

Included conditions:
- Parkinson Disease

Study Armgroups:
- {'label': "Parkinson's disease patients", 'description': "150 de novo treatment naive Parkinson's disease patients."}
- {'label': 'Healthy control subjects', 'description': '150 Healthy sex- and age-matched controls, also matched according to presence and severity of constipation, serving as a control group for microbiome composition analyses.'}

Interventions:

Primary Outcomes:
- {'measure': '[18F]FEOBV PET', 'description': 'Cortical and subcortical cholinergic innervation as measured by \\[18F\\] FEOBV PET imaging', 'timeFrame': 'Baseline'}

Please estimate the sample size based on the assumption: 
For the vision domain, an effect size of 0.45, an alpha of 0.05, and a power of 0.80 were assumed. The sample size also accounts for a dropout rate, with 180 participants included at baseline to ensure 150 participants after accounting for 30 drop-outs and non-PD cases.
Sample size
        Since most objectives of the DUPARC cohort study concern a first assessment in treatment-naÃ¯ve de novo PD subjects, a formal power calculation is hampered, as no adequate estimation of the expected effect sizes can be provided. However, the effect sizes previously reported in already treated PD subjects with longer disease duration are mostly expected to be larger than the effect sizes in our cohort. Therefore, a power calculation based on previous reports will provide us with a minimum number of participants to include, to assess the most important endpoints within the domains of cognition, gastrointestinal function and vision.
        The primary objective related to the cognitive domain is to establish the relationship between cognitive impairment and pre-synaptic cholinergic degeneration in de novo PD patients. This will be analyzed using cholinergic PET-imaging with FEOBV in combination with neuropsychological assessments covering all cognitive domains, including complex attention, learning and memory, executive function, perceptual-motor function, language, and social cognition. Because of the novelty of FEOBV, previous research using FEOBV-PET in PD is limited. Significant results were found in a small group comparing PD and control subjects [18]. Cross-sectional comparisons between PD subgroups have included between 15 and 79 PD patients, with significant results [42]. The size of the DUPARC cognition data is therefore expected to be sufficient for group and sub-group analyses, as well as detailed correlational research on the specific cognitive domains. Because of the great heterogeneity at baseline in both cognitive performance and cortical cholinergic innervation in PD, such a large cohort is needed for correlational analyses [43, 44].
        The main objective within the gastrointestinal function domain is the comparison of the gut microbiome composition with HC. Though a power calculation for metagenomic analyses is not possible, we think our sample size will be sufficient to do these analyses, because previous studies already reported significant differences with far smaller sample sizes varying between 10 and 72 included PD subjects. Only two treatment-naÃ¯ve subgroups of 12 and 39 PD subjects have been investigated in previous studies, reporting fewer taxonomic differences in the treatment-naÃ¯ve group, compared to already treated subjects. The DUPARC gut microbiome data therefore surpasses most PD gut microbiome studies in sample size, and is by far the largest treatment-naÃ¯ve dataset, allowing for more robust microbiome composition signatures and correction for confounders.
        Regarding the domain of vision, the most recent meta-analysis on OCT imaging in PD has reported overall mean effect sizes of 0.45 for several retinal cell layers, comparing HC to PD subjects [33]. For a similar effect size, with an alpha of 0.05, and a two-tailed comparison of means, a sample size of 79 subjects for each group would be sufficient to achieve a power of 0.80.
        The sample size of 150 participants therefore clearly surpasses the expected numbers needed to assess the primary objectives within the key domains of DUPARC. Nevertheless, a sample size of 150 participants is still necessary, as the anticipated effect sizes of various biomarkers in treatment-naÃ¯ve de novo PD subjects is expected to be lower, compared to treated PD subjects with longer disease duration. In addition, to find biomarkers indicative of PD subtypes, the PD sample not only has to provide both case and control samples for a subtype comparison, but also the intergroup differences are expected to be lower if PD subgroups are compared. Our sample size of 150 participants will most likely allow for binary and trinary subtype comparisons, given the aforementioned samples sizes required to distinguish PD from HC. Lastly, the sample size also needs to be larger than calculated to account for participants who will be lost to follow-up. For this purpose, 180 participants will be included at baseline to account for 30 drop-outs and non-PD cases, in order to ensure a sample size of 150 participants.