Here is the design of a clinical trial:

Official Title: Cost-effectiveness of Small Size Interarcuair Decompression Versus Extended Decompression in Patients With Intermittent Neurogenic Claudication (Size-study): a Multi-center, Double-blinded Randomized Controlled Trial

Included conditions:
- Stenoses, Spinal

Study Armgroups:
- {'label': 'Small size interarcuair decompression', 'type': 'EXPERIMENTAL', 'description': 'Patients will undergo small size interarcuair decompression', 'interventionNames': ['Procedure: small size interarcuair decompression']}
- {'label': 'Laminectomy', 'type': 'ACTIVE_COMPARATOR', 'description': 'Patients will undergo laminectomy', 'interventionNames': ['Procedure: Laminectomy']}

Interventions:
- {'type': 'PROCEDURE', 'name': 'small size interarcuair decompression', 'description': "A median lumbar incision is made and the paravertebral muscles are dissected subperiosteally and retracted unilaterally or bilaterally. Decompression will be applied via decompression of the ligamentum flavum. The lateral recess will be opened bilaterally and a medial facetectomy will be performed in order maintain stability of the segments. Posterior ligaments will be spared. The wound will be closed in layers with or without a suction drain. Patients will be operated with a loupe magnification or microscope depending on the surgeon's preference.", 'armGroupLabels': ['Small size interarcuair decompression']}
- {'type': 'PROCEDURE', 'name': 'Laminectomy', 'description': "A median lumbar incision is made over the spinous processes, the laminae of the affected level(s) are exposed subperiosteally, and the supraspinous ligament will be incised. The spinous process is removed. The supra and interspinous ligament of the affected level is removed by drill or Kerrison punches. The lamen is removed of the affect level, leaving the facet joint intact. The lateral recess will be opened bilaterally and medial facetectomy will be performed in order to maintain stability of the segments. When a single level stenosis is present (e.g. L4-L5) both laminae L4 and L5 will be removed. The wound will be closed in layers with or without a suction drain. Patients will be operated with loupe magnification or microscope depending surgeon's preference.", 'armGroupLabels': ['Laminectomy']}

Primary Outcomes:
- {'measure': 'Change on the Modified Roland-Morris Disability Questionnaire', 'description': 'This is a 24-point Dutch questionnaire that is designed to assess the physical disability in patients, due to lower back pain.', 'timeFrame': 'baseline, 3 weeks, 6 weeks, 12 weeks, 6 months, 12 months, 18 months, 24 months, 36 months and 48 months after surgery'}

Please estimate the sample size based on the assumption: 
The study uses a significance level (alpha) of 0.05, a power of 90%, and accounts for a 20% loss in follow-up.
Sample size
        The sample size of this study is calculated for the primary endpoint of group difference in the RMDQ at 12 months. According to literature, results obtained after interarcuair decompression should be 3 points lower on the RMDQ compared with those for the laminectomy group in order to detect superiority.45

        Hence, the sample size of this study is based on a superiority design, using a delta of 3, an assumed true mean difference of 0 and a pooled SD of 6. Using an alpha of 0.05, and a power of 90%, we calculated a sample size of 69 patients per group. Accounting for a 20% loss in follow-up, we will therefore enrol 174 patients (87 patients per group).