The Country Anatomy of CT.gov Transparency Gaps: A Fourteen-Lens Audit of 249,507 Older Closed Interventional Studies

Abstract

ClinicalTrials.gov hosts the world's largest public registry of clinical research, yet a substantial share of older closed studies remain silent — posting no results, no linked publications, and no endpoint descriptions. Whether this silence is geographically structured, and in what ways, remains poorly characterised. We conducted fourteen pre-specified analyses of 249,507 eligible older closed interventional studies drawn from the March 29, 2026 full-registry snapshot, measuring country-linked transparency across nine distinct gap dimensions: ancient backlog, description black-box, detailed-description gap, enrollment gap, composite excess watchlist, ghost-protocol excess, narrative gap, overdue debt, primary-only gap, primary-outcome gap, country-linked sponsor concentration, text asymmetry, and U.S.-versus-ex-U.S. sponsor-class stratification. The United States dominated absolute stock tables on every dimension by virtue of registry scale; rate tables revealed a different and smaller group of countries — Iran, Japan, France, South Korea, Egypt, Norway, Slovakia — each leading on different gap dimensions. The most policy-salient finding was the jurisdictional divide: studies involving at least one U.S. site carried a 52.1% no-results rate versus 88.7% for studies with no U.S. involvement, a 36.7-percentage-point gap consistent with the regulatory reach of the FDA Amendments Act. Disease and geography interact non-additively: oncology studies involving China reached 79.0% no results versus 52.6% for those involving the United States, and cardiovascular studies involving Egypt reached 95.9%. No single country or metric captures the problem; the geography of transparency failure is multidimensional.