Clinical Research ← pillar
├── Clinical Trial ← major pillar
│ ├── Phase I
│ ├── Phase II
│ ├── Randomization
│ ├── Blinding
│ ├── CRF
│ └── …
└── Clinical Study ← supporting/terminology article

Clinical Research should remain the highest-level conceptual page because it encompasses all research involving humans (and, depending on your scope, may discuss translational and observational research). Clinical Trial should be the operational pillar for the clinical trials domain, while Clinical Study serves primarily to clarify terminology and direct readers to the appropriate concepts.