Paper
Declared intervention type is not cosmetic metadata. It separates the registry into materially different transparency regimes.
Which intervention types look quietest on ClinicalTrials.gov once older closed interventional studies are grouped by declared intervention family? We analysed 249,507 eligible older closed interventional studies from the March 29, 2026 full-registry snapshot and merged raw intervention-type labels from the registry snapshot. The project compares two-year no-results rates, ghost-protocol rates, full visibility, and single-versus-multi-type contrasts across drug, device, behavioral, procedure, biological, dietary-supplement, and other intervention families. Drug studies form the largest family at 118,202 studies and show a 62.6 percent no-results rate. Dietary-supplement studies reach 90.6 percent no results, procedure studies 85.3 percent, while biological studies fall to 58.5 percent and multi-type studies outperform single-type studies. Declared intervention family therefore behaves like a strong visibility classifier rather than a cosmetic label inside the registry. The contrast persists even when large drug stock dominates the overall denominator across older studies. Studies can carry multiple intervention types and labels are sponsor-entered registry categories rather than audited therapeutic taxonomies.