Core Outcome Measures in Effectiveness Trials

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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’. 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.

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 536 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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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 22 July, 2014 - The COMET Initiative database: progress and activities from 2011 to 2013

    The Core Outcome Measures in Effectiveness Trials (COMET) Initiative database is an international repository of studies relevant to the development of core outcome sets. By the end of 2013, it included a unique collection of 306 studies. The website is increasingly being used, with more than 12,000 visits in 2013 (a 55% increase over 2012), 8,369 unique visitors (a 53% increase) and 6,844 new visitors (a 48% increase). There has been a rise in visits from outside the United Kingdom, with 2,405 such visits in 2013 (30% of all visits). By December 2013, a total of 4,205 searches had been completed, with 2,139 in 2013 alone In this letter we outline activities and progress related to the COMET website and database up to 31 December 2013 (source of data usage: Google Analytics).

  • Monday 21 July, 2014 - COMET in the news

    Understanding and Improving Clinical Trial Outcome Measures in Acute Respiratory Failure

    Read More: http://www.atsjournals.org/doi/abs/10.1164/rccm.201402-0362ED#.U80cwLHy18E
  • Thursday 19 June, 2014 - Choosing Important Health Outcomes for Comparative Effectiveness Research: A Systematic Review

    A total of 250 reports relating to 198 studies were judged eligible for inclusion in the review. Studies covered various areas of health, most commonly cancer, rheumatology, neurology, heart and circulation, and dentistry and oral health. A variety of methods have been used to develop COS. This systematic review identified many health areas where a COS has been developed, but also highlights important gaps. It is a further step towards a comprehensive, up-to-date database of COS. In addition, it shows the need for methodological guidance, including how to engage key stakeholder groups, particularly members of the public. Read the full review here.

Recently Added Studies

  • Development of a core outcome set (COS) for non-minimal-invasive on-pump cardiothoracic clinical trials

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  • Recommended patient-reported core set of symptoms to measure in adult cancer treatment trials

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  • Recommended patient-reported core set of symptoms and quality-of-life domains to measure in ovarian cancer treatment trials

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  • Recommended patient-reported core set of symptoms to measure in prostate cancer treatment trials

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  • Recommended patient-reported core set of symptoms to measure in head and neck cancer treatment trials

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