Previously unidentified duplicate registrations of clinical trials: an exploratory analysis of registry data worldwide

Abstract

BackgroundTrial registries were established to combat publication bias by creating a comprehensive and unambiguous record of initiated clinical trials. However, the proliferation of registries and registration policies means that a single trial may be registered multiple times (i.e., “duplicates”). Because unidentified duplicates threaten our ability to identify trials unambiguously, we investigate to what degree duplicates have been identified across registries globally.MethodsWe retrieved all records from the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) search portal and made a list of all records identified as duplicates by the ICTRP. To investigate how to discriminate duplicates from non-duplicates, we applied text-based similarity scoring to various registration fields of both ICTRP-identified duplicates and arbitrary pairs of trials. We then used the best similarity measure to identify the most similar pairs of records and manually assessed a random sample of pairs not identified as duplicates by the ICTRP to estimate the number of previously unidentified (or “hidden”) duplicates.ResultsTwo hundred eighty-five thousand unique records, or 271 thousand unique trials after accounting for known duplicates, were retrieved from the ICTRP portal in April 2015. We found that the title field best discriminated duplicates from non-duplicates. Out of 41 billion total pair-wise comparisons, we identified the 474,000 pairs of titles with the highest similarity scores (>0.5). After manually assessing a random sample of 434 pairs, we estimated that 45 % of all duplicate registrations currently go undetected and remain to be identified and confirmed as duplicates. Thus, the actual number of unique trials represented in this dataset is estimated to be approximately 258,000 (5 % less).ConclusionsThe ICTRP portal does not currently enable the unambiguous identification of trials across registries. Further research is needed to identify and verify the duplicates that currently go undetected. Sponsors, registries, and the ICTRP should consider actions to ensure duplicate registrations are easily identifiable.Electronic supplementary materialThe online version of this article (doi:10.1186/s13643-016-0283-8) contains supplementary material, which is available to authorized users.

Clinical trial transparency update: an assessment of the disclosure of results of company-sponsored trials associated with new medicines approved in Europe in 2014

“…We found that duplication with other registries is increasing, particularly with the European registry EudraCT, and observed that some trials were routinely registered multiple times, and regularly on ClinicalTrials.gov, EudraCT and a company's own registry when available. If all corresponding trial identifiers are cross referenced then duplicate registry records are easily identified, although it has been estimated that approximately 45% of all duplicate registrations on the WHO ICTRP currently go undetected, corresponding to a reduction in the number of unique records on the portal by approximately 5% 12 . Duplicates could affect the assessment of bias by inflating the number of trials that do not publish results and policy makers, trial sponsors and registries are encouraged to enact policies and quality assurance processes to improve the quality of published records 12 .…”

“…If all corresponding trial identifiers are cross referenced then duplicate registry records are easily identified, although it has been estimated that approximately 45% of all duplicate registrations on the WHO ICTRP currently go undetected, corresponding to a reduction in the number of unique records on the portal by approximately 5% 12 . Duplicates could affect the assessment of bias by inflating the number of trials that do not publish results and policy makers, trial sponsors and registries are encouraged to enact policies and quality assurance processes to improve the quality of published records 12 . While authors and trial sponsors must provide accurate data associated with each trial's unique identifier, registries and journals share responsibility for ensuring the accuracy of the public information they provide, including any automatic links.…”

Update on Trial Registration 11 Years after the ICMJE Policy Was Established

“…Total number of initiated, ongoing, and completed trials worldwide unknown WHO ICTRP Search Portal listed 323,018 study records from 16 trial registries (as of March 7, 2016; Table 1), of which 15,808 registrations identified by WHO ICTRP as “duplicates” (i.e., records from two or more registries representing a single trial)208,665 of the 307,210 (68%) WHO ICTRP-identified unique study records were registered on ClinicalTrials.govRecently estimated additional duplicate registrations not detected by the WHO ICTRP Search Portal 12 Unidentified duplicates create residual ambiguity when attempting to ascertain a definitive list of all trials on a given topic…”

“…Recently estimated additional duplicate registrations not detected by the WHO ICTRP Search Portal 12 …”

Standards for design and measurement would make clinical research reproducible and usable

“…• Penalties enforced for noncompliance with registration requirements • Trial registries define minimum data elements, including standards for defining outcomes (54,55) • Some trials are registered more than once (58) • Completed studies registered retrospectively • Completed ("legacy") trials were not covered by current requirements Research protocol…”