Searching clinical trials registers: guidance and recommendations for systematic reviewers
2Methods in Evidence Synthesis Unit, School of Public Health and Preventive Medicine, Monash University, Australia
3Health Technology Assessment Team, NHMRC Clinical Trials Centre, University of Sydney, Australia
4Centre for Health Communication and Participation, La Trobe University, Australia
Background: Clinical trial registers provide information on planned, ongoing and completed trials, both published and unpublished. Gold standard systematic reviews mandate searching trial registers since it allows retrieval of unpublished information, thereby reducing publication bias, research waste, and improving reliability of the generated evidence. However, searching trial registers is often challenging and guidance is lacking.
Objectives: We aimed to address this gap by providing step-by-step guidance on how to search clinical trial registers to harness their full potential.
Methods: We developed guidance based on 1) a literature review, 2) information available on trial registry websites, 3) a consensus workshop with information specialists, trial registry staff and systematic reviewers collating their experiences and expert opinions, and 4) an online survey of Cochrane information specialists and health technology assessment reviewers.
Results: We derived several key steps encompassing guidance for where to search, formulating the search strategy, conducting the search, screening registration records, obtaining data, and updating and reporting searches (Fig 1). For each step we highlight key differences to searching bibliographic databases, demonstrate practical application using a case study, and offer recommendations such as: which registers to search (World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) and ClinicalTrials.gov as a minimum); avoid using filters (e.g. by participant age or study type); and adjust search strategies for each registry.
Conclusions: Clinical trial registers are rich in data and this guidance outlines how best to find and harvest trial information from them. The recommendations can be used to retrieve unpublished results data directly from the registry or via communication with registrants. They may also facilitate identification of evidence gaps to inform research prioritisation, identification of ongoing trials for collaborative methodologies such as prospective meta-analysis, assessment of publication bias, and planning of updates of traditional or living systematic reviews.
Patient, public and/or healthcare consumer involvement: This guidance was tested by two first-time registry users as well as several experienced systematic reviewers. Implementation of these methods will help to streamline evidence synthesis, reduce bias, and enhance the reliability and validity of systematic reviews, ultimately leading to better health outcomes.