Paper
Blank or underspecified purpose fields are one of the clearest structural warning signs in the registry.
Which primary purposes look quietest on ClinicalTrials.gov once older closed interventional studies are grouped by stated design intent? We analysed 249,507 eligible older closed interventional studies from the March 29, 2026 full-registry snapshot and compared sponsor-entered purpose and allocation fields. The project estimates two-year no-results rates, ghost-protocol rates, full visibility, and allocation contrasts across treatment, prevention, diagnostic, supportive-care, and unlabeled purpose groups. Treatment trials showed a 68.3 percent no-results rate and a 40.5 percent ghost-protocol rate. Trials with no recorded primary purpose rose to 86.4 percent no results and 59.2 percent ghost protocols, while device-feasibility studies also remained highly obscured. Design intent therefore matters, and blank or underspecified purpose fields mark especially quiet registry segments. Unlabeled intent behaves like a durable warning sign for weak public documentation and low disclosure across sponsors and phases alike. Primary-purpose and allocation fields are sponsor-entered labels rather than externally audited design adjudications, so the analysis remains registry-structural rather than legal.