Name of trial registry, identifying number (with URL) and date of registration
Example
“This study was registered in the Iranian Registry of Clinical Trials under the code IRCT20150531022498N30: https://en.irct.ir/trial/41031. Registered on July 26, 2019.”1
Explanation
The consequences of non-publication of entire trials (ie, publication bias),2–4 and of selective reporting of outcomes and analyses within trials, have been well documented.5,67 For almost 40 years, there have been growing calls to address these practices. Today, a ubiquitous view recommends trial registration as the best practice to achieve this goal, and inform policymakers and potential participants about ongoing trials. Registering clinical trials, before any assignment of participants, with unique trial identification numbers and other basic information about the trial so that essential details are made publicly available, is a minimum best practice.8–11 Serious problems of withholding data12 led to renewed efforts to ensure registration of randomised trials. The World Health Organization (WHO) states that “the registration of all interventional trials is a scientific, ethical and moral responsibility.”13
In September 2004, the ICMJE established a policy that it would only consider trials for publication if they had been registered before the enrolment of the first participant.14 This policy resulted in a substantial increase in the number of trials being registered.15 However, some trials are still not registered.3 The ICMJE gives guidance on acceptable registries and also accepts registration in WHO primary registries and ClinicalTrials.gov. Registers charging a fee to view their content should be avoided to ensure equity of access for everyone, including patients and the public.
The Transparency and Openness Promotion (TOP) guidelines, endorsed and used by thousands of journals, recommends trial registration.16 In a survey of 168 high impact factor medical journals’ “Instructions to authors” in 2014, 78 journals stated that all recent clinical trials must be registered as a requirement of submission to that journal.17 A more recent survey in 2019 of surgical journals publishing randomised trials found that 53 of 82 journals mandated prospective registration.18
Despite recommendations, and mandates in some jurisdictions for clinical trialists to register their trial and evidence that registration deters selective reporting, this is still not happening universally.1920 Authors should provide the name of the registry, the trial’s associated registration number, date of registration and, where possible, the URL for the trial’s registration. We recommend that authors also report whether (or when) the trial results are available on the associated trial register.
Despite the considerable increase in clinical trial registration, there is a strong body of evidence showing the lack of access to trial results.21–24 The latest version of the Declaration of Helsinki states that “Researchers have a duty to make publicly available the results of their research on human participants and are accountable for the timeliness, completeness, and accuracy of their reports . . . Negative and inconclusive as well as positive results must be published or otherwise made publicly available.” In 2015, WHO published a new statement on the public disclosure of trial results, which requests that “the key outcomes are to be made publicly available within 12 months of study completion by posting to the results section of the primary clinical trial registry. Where a registry is used without a results database available, the results should be posted on a free-to-access, publicly available, searchable institutional website of the Regulatory Sponsor, Funder or Principal Investigator.” Some legislations are also in place in the US, UK, and Europe requesting the posting of trial results on clinical trials registry within 12 months after study completion.25–27
Authors should indicate whether the trial results are publicly posted to the trial registry, as a preprint (with URL citation) or as published articles (with citations).
Training
The UK EQUATOR Centre runs training on how to write using reporting guidelines.
Discuss this item
Visit this items’ discussion page to ask questions and give feedback.
References
1.
Nazari M, Shabani R, Hassanzadeh-Rad A, Esfandiari MA, Dalili S. Effect of concurrent resistance-aerobic training on inflammatory factors and growth hormones in children with type 1 diabetes: A randomized controlled clinical trial. Trials. 2023;24(1). doi:10.1186/s13063-023-07553-0
2.
Dickersin. 1997;9.
3.
Jeffrey JD, Thorstensen MJ, Enders EC, Treberg JR, Jeffries KM. Using transcriptomics to examine the physiological status of wild-caught walleye (sander vitreus). Porter L, ed. FACETS. 2023;8:1-15. doi:10.1139/facets-2022-0177
4.
Riedel N, Wieschowski S, Bruckner T, et al. Results dissemination from completed clinical trials conducted at german university medical centers remained delayed and incomplete. The 2014 –2017 cohort. Journal of Clinical Epidemiology. 2022;144:1-7. doi:10.1016/j.jclinepi.2021.12.012
5.
Chan AW, Hróbjartsson A, Haahr MT, Gøtzsche PC, Altman DG. Empirical evidence for selective reporting of outcomes in randomized trials: Comparison of protocols to published articles. JAMA. 2004;291(20):2457. doi:10.1001/jama.291.20.2457
6.
Al-Marzouki S, Roberts I, Evans S, Marshall T. Selective reporting in clinical trials: Analysis of trial protocols accepted by the lancet. The Lancet. 2008;372(9634):201. doi:10.1016/s0140-6736(08)61060-0
7.
Williamson PR, Gamble C. Identification and impact of outcome selection bias in meta‐analysis. Statistics in Medicine. 2004;24(10):1547-1561. doi:10.1002/sim.2025
8.
Simes RJ. Publication bias: The case for an international registry of clinical trials. Journal of Clinical Oncology. 1986;4(10):1529-1541. doi:10.1200/jco.1986.4.10.1529
9.
Chalmers I. From optimism to disillusion about commitment to transparency in the medico-industrial complex. Journal of the Royal Society of Medicine. 2006;99(7):337-341. doi:10.1177/014107680609900715
10.
Tonks A. A clinical trials register for europe. BMJ. 2002;325(7376):1314-1315. doi:10.1136/bmj.325.7376.1314
11.
Dickersin K. Registering clinical trials. JAMA. 2003;290(4):516. doi:10.1001/jama.290.4.516
12.
Whittington CJ, Kendall T, Fonagy P, Cottrell D, Cotgrove A, Boddington E. Selective serotonin reuptake inhibitors in childhood depression: Systematic review of published versus unpublished data. The Lancet. 2004;363(9418):1341-1345. doi:10.1016/s0140-6736(04)16043-1
13.
World health organization . International standards for clinical trial registries: The registration of all interventional trials is a scientific, ethical and moral responsibility. 3rd ed. World health organization, 2018.
14.
De Angelis CD, Drazen JM, Frizelle FA, et al. Is this clinical trial fully registered? A statement from the international committee of medical journal editors. The Lancet. 2005;365(9474):1827-1829. doi:10.1016/s0140-6736(05)66588-9
15.
Zarin DA, Ide NC, Tse T, Harlan WR, West JC, Lindberg DAB. Issues in the registration of clinical trials. JAMA. 2007;297(19):2112. doi:10.1001/jama.297.19.2112
16.
Nosek BA, Alter G, Banks GC, et al. Promoting an open research culture. Science. 2015;348(6242):1422-1425. doi:10.1126/science.aab2374
17.
Shamseer L, Hopewell S, Altman DG, Moher D, Schulz KF. Update on the endorsement of CONSORT by high impact factor journals: A survey of journal “instructions to authors” in 2014. Trials. 2016;17(1). doi:10.1186/s13063-016-1408-z
18.
Lombard N, Gasmi A, Sulpice L, Boudjema K, Naudet F, Bergeat D. Research transparency promotion by surgical journals publishing randomised controlled trials: A survey. Trials. 2020;21(1). doi:10.1186/s13063-020-04756-7
19.
Trinquart L, Dunn AG, Bourgeois FT. Registration of published randomized trials: A systematic review and meta-analysis. BMC Medicine. 2018;16(1). doi:10.1186/s12916-018-1168-6
20.
Chan AW, Pello A, Kitchen J, et al. Association of trial registration with reporting of primary outcomes in protocols and publications. JAMA. 2017;318(17):1709. doi:10.1001/jama.2017.13001
21.
Chan AW, Song F, Vickers A, et al. Increasing value and reducing waste: Addressing inaccessible research. The Lancet. 2014;383(9913):257-266. doi:10.1016/s0140-6736(13)62296-5
22.
DeVito NJ, Bacon S, Goldacre B. Compliance with legal requirement to report clinical trial results on ClinicalTrials.gov: A cohort study. The Lancet. 2020;395(10221):361-369. doi:10.1016/s0140-6736(19)33220-9
23.
DeVito NJ, Morley J, Smith JA, Drysdale H, Goldacre B, Heneghan C. Availability of results of clinical trials registered on EU clinical trials register: Cross sectional audit study. BMJ Medicine. 2024;3(1):e000738. doi:10.1136/bmjmed-2023-000738
24.
Pellat A, Boutron I, Ravaud P. Availability of results of trials studying pancreatic adenocarcinoma over the past 10 years. The Oncologist. 2022;27(11):e849-e855. doi:10.1093/oncolo/oyac156
25.
Moorthy VS, Karam G, Vannice KS, Kieny MP. Rationale for WHO’s new position calling for prompt reporting and public disclosure of interventional clinical trial results. PLOS Medicine. 2015;12(4):e1001819. doi:10.1371/journal.pmed.1001819
26.
Food and drug administration amendments act of 2007. Public law 110-85. Https://www.govinfo.gov/app/details/PLAW-110publ85 d [accessed 17 september 2024]. 2007.
27.
2012;55.
Reuse
Most of the reporting guidelines and checklists on this website were originally published under permissive licenses that allowed their reuse. Some were published with propriety licenses, where copyright is held by the publisher and/or original authors. The original content of the reporting checklists and explanation pages on this website were drawn from these publications with knowledge and permission from the reporting guideline authors, and subsequently revised in response to feedback and evidence from research as part of an ongoing scholarly dialogue about how best to disseminate reporting guidance. The UK EQUATOR Centre makes no copyright claims over reporting guideline content. Our use of copyrighted content on this website falls under fair use guidelines.
Citation
For attribution, please cite this work as:
Hopewell S, Chan AW, Collins GS, et al. CONSORT
2025 statement: updated guideline for reporting randomised trials.
BMJ. 2025;389:e081123. doi:10.1136/bmj-2024-081123
Reporting Guidelines are recommendations to help describe your work clearly
Your research will be used by people from different disciplines and backgrounds for decades to come. Reporting guidelines list the information you should describe so that everyone can understand, replicate, and synthesise your work.
Reporting guidelines do not prescribe how research should be designed or conducted. Rather, they help authors transparently describe what they did, why they did it, and what they found.
Reporting guidelines make writing research easier, and transparent research leads to better patient outcomes.
Easier writing
Following guidance makes writing easier and quicker.
You work will be read by different people, for different reasons, around the world, and for decades to come. Reporting guidelines help you consider all of your potential audiences. For example, your research may be read by researchers from different fields, by clinicians, patients, evidence synthesisers, peer reviewers, or editors. Your readers will need information to understand, to replicate, apply, appraise, synthesise, and use your work.
Cohort studies
A cohort study is an observational study in which a group of people with a particular exposure (e.g. a putative risk factor or protective factor) and a group of people without this exposure are followed over time. The outcomes of the people in the exposed group are compared to the outcomes of the people in the unexposed group to see if the exposure is associated with particular outcomes (e.g. getting cancer or length of life).
A case-control study is a research method used in healthcare to investigate potential risk factors for a specific disease. It involves comparing individuals who have been diagnosed with the disease (cases) to those who have not (controls). By analysing the differences between the two groups, researchers can identify factors that may contribute to the development of the disease.
An example would be when researchers conducted a case-control study examining whether exposure to diesel exhaust particles increases the risk of respiratory disease in underground miners. Cases included miners diagnosed with respiratory disease, while controls were miners without respiratory disease. Participants' past occupational exposures to diesel exhaust particles were evaluated to compare exposure rates between cases and controls.
A cross-sectional study (also sometimes called a "cross-sectional survey") serves as an observational tool, where researchers capture data from a cohort of participants at a singular point. This approach provides a 'snapshot'— a brief glimpse into the characteristics or outcomes prevalent within a designated population at that precise point in time. The primary aim here is not to track changes or developments over an extended period but to assess and quantify the current situation regarding specific variables or conditions. Such a methodology is instrumental in identifying patterns or correlations among various factors within the population, providing a basis for further, more detailed investigation.
A systematic review is a comprehensive approach designed to identify, evaluate, and synthesise all available evidence relevant to a specific research question. In essence, it collects all possible studies related to a given topic and design, and reviews and analyses their results.
The process involves a highly sensitive search strategy to ensure that as much pertinent information as possible is gathered. Once collected, this evidence is often critically appraised to assess its quality and relevance, ensuring that conclusions drawn are based on robust data. Systematic reviews often involve defining inclusion and exclusion criteria, which help to focus the analysis on the most relevant studies, ultimately synthesising the findings into a coherent narrative or statistical synthesis. Some systematic reviews will include a [meta-analysis]{.defined data-bs-toggle="offcanvas" href="#glossaryItemmeta_analyses" aria-controls="offcanvasExample" role="button"}.
A randomised controlled trial (RCT) is a trial in which participants are randomly assigned to one of two or more groups: the experimental group or groups receive the intervention or interventions being tested; the comparison group (control group) receive usual care or no treatment or a placebo. The groups are then followed up to see if there are any differences between the results. This helps in assessing the effectiveness of the intervention.
Research that aims to gather and analyse non-numerical (descriptive) data in order to gain an understanding of individuals' social reality, including understanding their attitudes, beliefs, and motivation. This type of research typically involves in-depth interviews, focus groups, or field observations in order to collect data that is rich in detail and context. Qualitative research is often used to explore complex phenomena or to gain insight into people's experiences and perspectives on a particular topic. It is particularly useful when researchers want to understand the meaning that people attach to their experiences or when they want to uncover the underlying reasons for people's behaviour. Qualitative methods include ethnography, grounded theory, discourse analysis, and interpretative phenomenological analysis.
Diagnostic accuracy studies focus on estimating the ability of the test(s) to correctly identify people with a predefined target condition, or the condition of interest (sensitivity) as well as to clearly identify those without the condition (specificity).
Prediction Models
Prediction model research is used to test the accurarcy of a model or test in estimating an outcome value or risk. Most models estimate the probability of the presence of a particular health condition (diagnostic) or whether a particular outcome will occur in the future (prognostic). Prediction models are used to support clinical decision making, such as whether to refer patients for further testing, monitor disease deterioration or treatment effects, or initiate treatment or lifestyle changes. Examples of well known prediction models include EuroSCORE II for cardiac surgery, the Gail model for breast cancer, the Framingham risk score for cardiovascular disease, IMPACT for traumatic brain injury, and FRAX for osteoporotic and hip fractures.
Quality improvement research is about finding out how to improve and make changes in the most effective way. It is about systematically and rigourously exploring "what works" to improve quality in healthcare and the best ways to measure and disseminate this to ensure positive change. Most quality improvement effectiveness research is conducted in hospital settings, is focused on multiple quality improvement interventions, and uses process measures as outcomes. There is a great deal of variation in the research designs used to examine quality improvement effectiveness.
A meta-analysis is a statistical technique that amalgamates data from multiple studies to yield a single estimate of the effect size. This approach enhances precision and offers a more comprehensive understanding by integrating quantitative findings. Central to a meta-analysis is the evaluation of heterogeneity, which examines variations in study outcomes to ensure that differences in populations, interventions, or methodologies do not skew results. Techniques such as meta-regression or subgroup analysis are frequently employed to explore how various factors might influence the outcomes. This method is particularly effective when aiming to quantify the effect size, odds ratio, or risk ratio, providing a clearer numerical estimate that can significantly inform clinical or policy decisions.
How Meta-analyses and Systematic Reviews Work Together
Systematic reviews and meta-analyses function together, each complementing the other to provide a more robust understanding of research evidence. A systematic review meticulously gathers and evaluates all pertinent studies, establishing a solid foundation of qualitative and quantitative data. Within this framework, if the collected data exhibit sufficient homogeneity, a meta-analysis can be performed. This statistical synthesis allows for the integration of quantitative results from individual studies, producing a unified estimate of effect size. Techniques such as meta-regression or subgroup analysis may further refine these findings, elucidating how different variables impact the overall outcome. By combining these methodologies, researchers can achieve both a comprehensive narrative synthesis and a precise quantitative measure, enhancing the reliability and applicability of their conclusions. This integrated approach ensures that the findings are not only well-rounded but also statistically robust, providing greater confidence in the evidence base.
Why Don't All Systematic Reviews Use a Meta-Analysis?
Systematic reviews do not always have meta-analyses, due to variations in the data. For a meta-analysis to be viable, the data from different studies must be sufficiently similar, or homogeneous, in terms of design, population, and interventions. When the data shows significant heterogeneity, meaning there are considerable differences among the studies, combining them could lead to skewed or misleading conclusions. Furthermore, the quality of the included studies is critical; if the studies are of low methodological quality, merging their results could obscure true effects rather than explain them.
Protocol
A plan or set of steps that defines how something will be done. Before carrying out a research study, for example, the research protocol sets out what question is to be answered and how information will be collected and analysed.
