Paper
The registry backlog is not evenly distributed across sponsors, even though it spans many sectors and institutions.
Is the ClinicalTrials.gov missing-results backlog spread evenly across sponsors, or does a relatively small slice hold most of the unresolved stock? We analysed sponsor-level counts for 249,507 eligible older closed interventional studies and ranked 25,584 lead sponsors by two-year missing-results volume. The concentration analysis tracked cumulative shares of unresolved no-results studies, sponsor-level ghost-protocol counts, and inequality metrics alongside named outlier sponsors. The top 1 percent of lead sponsors accounted for 39.6 percent of the missing-results backlog, and the top 10 percent accounted for 77.4 percent. The sponsor-level Gini coefficient reached 0.818, while large industry firms, major academic centers, and public institutions all appeared among the highest-volume sponsors. The unresolved stock is therefore broad but highly uneven, with a thin sponsor slice carrying a disproportionate share of what remains unseen. These concentration statistics describe registry-visible stock distribution, not legal liability, and they depend on the lead-sponsor field recorded in CT.gov across this sponsor field and snapshot frame.