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 956 references of planned, ongoing and completed work.

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

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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

  • Tuesday 21 November, 2017 - Core Outcome Set-STAndards for Development: The COS-STAD recommendations

    Several hundred COS projects have been systematically identified to date, but there has been no formal quality assessment of these studies. The Core Outcome Set-STAndards for Development (COS-STAD) project aimed to identify minimum standards for the design of a COS study agreed upon by an international group. Read the full paper here.

    Other specific guidance exists for the final reporting of COS development studies (Core Outcome Set-STAndards for Reporting [COS-STAR]).

  • Wednesday 01 November, 2017 - The COMET Handbook: version 1.0

    Have you read the Handbook?

    This Handbook, developed by the COMET Initiative, brings together current thinking and methodological research regarding those issues. We recommend a four-step process to develop a core outcome set. The aim is to update the contents of the Handbook as further research is identified.

  • Thursday 23 February, 2017 - Do you have a consensus meeting planned or coming up?

    If you are planning an upcoming consensus meeting and would be happy for an early career researcher to observe the meeting in order to learn from the experience, please let us know.  This would be an invaluable opportunity to gain experience in the development of core outcome sets for potential COS developers. Please email info@comet-initiative.org

Recently Added Studies

  • Development of a Core Outcome Set for conservative and surgical interventions for elbow disorders (COSed)

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  • Development of Core Outcome Sets for Oesophageal Atresia

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  • Core outcomes for critical limb ischaemia

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  • Patient-reported outcomes of pain and physical functioning in neurofibromatosis clinical trials

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  • Rapid Review protocol for Post Operative Pain Outcome Measures Study (POPOS)

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