Paper
Simple protocol structure should not be mistaken for transparent public reporting.
How much does trial architecture shape ClinicalTrials.gov hiddenness once older closed interventional studies are grouped by arms and intervention counts? We analysed 249,507 eligible older closed interventional studies from the March 29, 2026 full-registry snapshot and grouped them by arm-group and intervention counts. The project compares two-year no-results rates, ghost-protocol rates, hiddenness scores, and phase-specific contrasts across simple and complex trial architectures. One-arm studies showed a 72.8 percent no-results rate, a 48.5 percent ghost-protocol rate, and a hiddenness score of 3.44. Studies with 10 or more arms fell to 55.3 percent no results, while one-intervention studies remained quieter than trials with larger intervention counts. Simpler-looking architectures are therefore not more transparent and often sit inside much quieter registry segments. That pattern holds in both early-phase work and later confirmatory programs with broader designs in practice today. Arm and intervention counts are registry structure fields and do not capture protocol nuance, adaptive features, or downstream analytic complexity.