CT.gov Hiddenness Atlas: What Sponsors Still Do Not Show

Abstract

Are sponsor groups related to the non-disclosure burden on ClinicalTrials.gov? Using the ClinicalTrials.gov API and a Python program (code shared for reproducibility), we analysed 578,109 registry records from 29 March 2026, including 441,191 interventional studies of which 290,524 were closed. We derived omission flags — missing results, missing actual completion dates, missing actual enrollment, absent IPD statements, sparse outcomes, and absent publication links — and summarised them by sponsor, sponsor class, and phase. Among older closed interventional studies, 72.7 percent had no posted results, with other-government (non-federal) worst at 95.7 percent and the OTHER class largest by volume at 127,704 studies. Industry still carried 44,007 two-year no-results studies, phase I had the highest non-reporting rate at 76.7 percent, and NIH had the highest average hiddenness score among named sponsor classes. Because registry opacity is concentrated differently by class, rates, volumes, and structural missingness must be read together. This measures registry-visible omission, not legal violation.