Comparison of Availability of Trial Results in ClinicalTrials.gov and PubMed by Funder Type and Trial Primary Completion Date

Julianne T. Nelson,1 Tony Tse,2 Yvonne Puplampu-Dove,1 Elisa Golfinopoulos,1 Deborah A. Zarin3


The proportion and timing of results available for registered clinical trials was examined by data source (ie, ClinicalTrials.gov and PubMed) and funder type. Prior work assessed PubMed-indexed publications for National Institutes of Health (NIH)–funded trials completed by 20081; published trial results, by academic and industry funder, with results posted on ClinicalTrials.gov in 20122; and industry- and nonindustry-funded trials completed by 2015 with published or posted results.3 This study updates prior work and appears to be the first analysis stratified by 4 funder types: NIH, non-NIH US federal agency, industry, and other (eg, foundation).


On August 1, 2021, a cross-sectional analysis was conducted of ClinicalTrials.gov-registered trials with at least 1 US facility, initiated on or after January 1, 2015, with primary completion dates (PCDs) up to August 1, 2018. A total of 100 trials from each key funder type was randomly sampled (Figure 13). To identify PubMed-indexed publications reporting primary outcomes between August 6 and October 8, 2021, 4 authors each reviewed registered information for 100 trials,1 and the fifth resolved ambiguities. The median time for follow-up from PCD was 47.8 months (IQR, 41.9-56.8 months). The proportion of trials with results, by data source and funder type, was determined, and time from PCD to first results availability was evaluated using Kaplan-Meier analysis with R.


Results were identified for 245 of 400 trials (61.3%) at least 36 months after PCD (57 trials with results available from both ClinicalTrials.gov and PubMed), with 98 of 245 (40.0%) and 147 of 245 (60.0%) first available on ClinicalTrials.gov and PubMed, respectively. Among these 245 records, the median time from PCD to first results availability was 22.1 months (IQR, 14.9-32.9 months) from either data source, 18.8 months (IQR, 13.4-29.3 months) to posting on ClinicalTrials.gov (n = 117), and 25.6 months (IQR, 18.6-36.3 months) to PubMed-indexed publication (n = 185). The proportions of trials with results available by key funder type were 60 of 100 (NIH), 71 of 100 (non-NIH US federal agency), 50 of 100 (industry), and 64 of 100 (other/foundation). Time to first results availability by funder type showed significant differences (P = .003) (Figure 13).


The finding that 40.0% of sampled trials (98 of 245) with results were posted on ClinicalTrials.gov before publication suggests that searching both data sources maximizes discovery of trial results, which is generally consistent with prior findings.2 Significant differences in proportion of results and time to first availability by key funder type suggest that sponsors and trialists may be affected by different factors based on funding source, such as policy and/or legal requirements. A better understanding of funding-specific factors could help improve overall results availability and timing. Larger sample sizes to validate these preliminary findings and research on the effectiveness of reporting requirements are needed. Finally, sampling trials conducted from January 2015 to August 2018 ensured recent initiation and allowed time for publication but excluded longer-running trials.


1. Ross JS, Tse T, Zarin DA, Xu H, Zhou L, Krumholz HM. Publication of NIH funded trials registered in ClinicalTrials.gov: cross-sectional analysis. BMJ. 2012;344:d7292. doi:10.1136/bmj.d7292

2. Riveros C, Dechartres A, Perrodeau E, Haneef R, Boutron I, Ravaud P. Timing and completeness of trial results posted at ClinicalTrials.gov and published in journals. PLoS Med. 2013;10(12):e1001566. doi:10.1371/journal.pmed.1001566

3. Zwierzyna M, Davies M, Hingorani AD, Hunter J. Clinical trial design and dissemination: comprehensive analysis of ClinicalTrials.gov and PubMed data since 2005. BMJ. 2018;361:k2130. doi:10.1136/bmj.k2130

1ICF, Bethesda, MD, USA, julianne.nelson@nih.gov; 2The National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD, USA; 3Multi-Regional Clinical Trials Center of Brigham and Women’s Hospital and Harvard, Cambridge, MA, USA

Conflict of Interest Disclosures

None reported.


This research was supported by the National Center for Biotechnology Information of the National Library of Medicine, National Institutes of Health.

Role of the Funder/Sponsor

The National Library of Medicine, National Institutes of Health supported the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the abstract; and decision to submit the abstract for presentation.

Additional Information

The views expressed in this abstract are those of the authors and do not necessarily reflect the views or policies of the National Institutes of Health. Tony Tse is a co–corresponding author.