Core Outcome Measures in Effectiveness Trials

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.

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 725 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

  • Monday 25 January, 2016 - Core outcome sets and systematic reviews

    Systematic reviews seek to bring together research evidence to answer the question for the review. The reviewers usually wish to compare, contrast and, if appropriate, combine the findings of the existing research studies. However, these intentions are often thwarted by inconsistencies in the outcomes that were measured and reported in the individual studies. This, in turn, makes it difficult for readers of the review to use it to make informed decisions and choices about health and social care. One solution is for trials in a particular topic area to measure and report a standardised set of outcomes, which would then be used in the review. Core outcome sets are a means of doing this. Read the full commentary here.

  • Monday 25 January, 2016 - Choosing Important Health Outcomes for Comparative Effectiveness Research: An Updated Review and User Survey

    This study aimed to provide an update of a previous review, and examine the quality of development of COS. A further aim was to understand the reasons why individuals are searching the COMET database. This update demonstrates that recent studies appear to have adopted a more structured approach towards COS development and public representation has increased. The pop-up survey revealed the most common reasons for visiting the COMET website to be thinking about developing a COS and planning a clinical trial. Read the full paper here.

  • Friday 13 November, 2015 - The COMET initiative database: progress and activities update (2014)

    The COMET Initiative database is a repository of studies relevant to the development of core outcome sets (COS). Use of the website continues to increase, with more than 16,500 visits in 2014 (36 % increase over 2013), 12,257 unique visitors (47 % increase), 9780 new visitors (43 % increase) and a rise in the proportion of visits from outside the UK (8565 visits; 51 % of all visits). By December 2014, a total of 6588 searches had been completed, with 2383 in 2014 alone (11 % increase). The growing awareness of the need for COS is reflected in the website and database usage figures. Read the full report here.

Recently Added Studies

  • Establishing a Core Outcome set for studies examining multimorbidity

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  • Core outcomes and common data elements for cervical degenerative myelopathy (CODE-CDH)

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  • Towards Improvement in Care Delivery in Huntington’s Disease (HD): ImproveHD

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  • Development of consensus standardised ‘Core’ Outcome Data set for disease modification in clinical trials for mild to moderate dementia (COD Dementia)

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  • Development of a core outcome set for clinical trials in Menière’s disease – a pilot survey of healthcare professionals and patients.

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