Core Outcome Measures in Effectiveness Trials

COMET Initiative

The COMET (Core Outcome Measures in Effectiveness Trials) Initiative brings together people interested in the development and application of agreed standardised sets of outcomes, known as ‘core outcome sets’ (COS). These sets represent the minimum that should be measured and reported in all clinical trials of a specific condition, and are also suitable for use in clinical audit or research other than randomised trials. The existence or use of a core outcome set does not imply that outcomes in a particular trial should be restricted to those in the relevant core outcome set. Rather, there is an expectation that the core outcomes will be collected and reported, making it easier for the results of trials to be compared, contrasted and combined as appropriate; while researchers continue to explore other outcomes as well. COMET aims to collate and stimulate relevant resources, both applied and methodological, to facilitate exchange of ideas and information, and to foster methodological research in this area. The COMET Handbook Version 1.0 is available here.

When searching the COMET database, please note that a systematic review is currently underway to identify eligible material, and we are continually updating the database as we identify eligible studies. Therefore, the records retrieved by any search might increase on a daily basis.


The COMET database currently contains 999 references of planned, ongoing and completed work.

The keyword used for the search will be compared with study title, abstract and author's surname.

View full search options

To view a demonstration of how to search the COMET database click here

Core resource pack


Useful references for core outcome set developers.

This includes an overview of the problems with outcomes in trials, key issues to consider in the development of a core outcome set, examples of core outcome set development, and things to think about once a COS is agreed. To read more, click here.

Latest News

  • Monday 19 February, 2018 - The BJD is embracing core outcome set development – why this is good news

    The BJD now has a dedicated section for qualitative and outcomes research, and has been a long-standing supporter of groups developing core outcome sets in dermatology. As such, it is no surprise to find the article by Horbach et al. in this issue's BJD, which outlines the first important steps on the journey towards a fully defined core outcome set for vascular malformations (OVAMA project). Read more here.

  • Monday 19 February, 2018 - An updated systematic review of COS

    The COMET (Core Outcome Measures in Effectiveness Trials) Initiative maintains an up to date, publicly accessible online database of published and ongoing COS. An annual systematic review update is an important part of this process. This review employed the same, multifaceted approach that was used in the original review and the previous two updates.

    Eighteen publications, relating to 15 new studies describing the development of 15 COS, were eligible for inclusion in the review. Results show an increase in the use of mixed methods, including Delphi surveys. Clinical experts remain the most common stakeholder group involved. Overall, only 16% of the 259 COS studies published up to the end of 2016 have included participants from LMICs.

  • Tuesday 06 February, 2018 - Improving global health clinical trials – where to begin?

    In the UK, the top three priorities in research methodologies for clinical trials have been identified as boosting recruitment, retention of participants and choosing outcomes to collect. But are these priorities the same in the rest of the world? In an effort to explore this, research published today in Trials surveyed researchers who have experience in trials in low to middle income countries. Here the authors tell us more.

Recently Added Studies

  • Protocol for the development of a global core outcome set for treatment of uncomplicated appendicitis in children

    [View details]
  • Heterogeneity in Definitions of Endpoints for Clinical Trials of Ulcerative Colitis: A Systematic Review for Development of a Core Outcome Set

    [View details]
  • Developing a core outcome set for studies on pregnant women with Vasa Previa

    [View details]
  • Development of a core outcome set for childhood epilepsy treated with ketogenic diet therapy.

    [View details]
  • Outcome Reporting in Randomized Trials for Shoulder Disorders: Literature Review to Inform the Development of a Core Outcome Set

    [View details]

Subscribe to the COMET mailing list

* indicates required

The site uses cookies, some may have been set already. Please refer to our privacy policy & cookie usage statement.
If you continue to use the site we'll assume you're happy to accept the cookies.