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Core Outcome Measures in Effectiveness Trials (COMET) initiative: protocol for an international Delphi study to achieve consensus on how to select outcome measurement instruments for outcomes included in a ‘core outcome set’

Cecilia A C Prinsen12*, Sunita Vohra34, Michael R Rose5, Susanne King-Jones3, Sana Ishaque3, Zafira Bhaloo3, Denise Adams3 and Caroline B Terwee12

Author Affiliations

1 Department of Epidemiology and Biostatistics, VU University Medical Center, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands

2 EMGO Institute for Health and Care Research, VU University Medical Center, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands

3 Department of Pediatrics, Faculty of Medicine and Dentistry, and School of Public Health, University of Alberta, Edmonton Continuing Care Center 8B19, 11111 Jasper Avenue, Edmonton, AB T5K 0L4, Canada

4 Women’s and Children’s Health Research Institute, University of Alberta, 4-081 Edmonton Clinic Health Academy (ECHA), 11405 - 87 Avenue, Edmonton, AB T6G 1C9, Canada

5 Department of Neurology, King’s College Hospital, Denmark Hill, London SE5 9RS, UK

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Trials 2014, 15:247  doi:10.1186/1745-6215-15-247

Published: 25 June 2014



The Core Outcome Measures in Effectiveness Trials (COMET) initiative aims to facilitate the development and application of ‘core outcome sets’ (COS). A COS is an agreed minimum set of outcomes that should be measured and reported in all clinical trials of a specific disease or trial population. The overall aim of the Core Outcome Measurement Instrument Selection (COMIS) project is to develop a guideline on how to select outcome measurement instruments for outcomes included in a COS. As part of this project, we describe our current efforts to achieve a consensus on the methods for selecting outcome measurement instruments for outcomes to be included in a COS.


A Delphi study is being performed by a panel of international experts representing diverse stakeholders with the intention that this will result in a guideline for outcome measurement instrument selection. Informed by a literature review, a Delphi questionnaire was developed to identify potentially relevant tasks on instrument selection. The Delphi study takes place in a series of rounds. In the first round, panelists were asked to rate the importance of different tasks in the selection of outcome measurement instruments. They were encouraged to justify their choices and to add other relevant tasks. Consensus was reached if at least 70% of the panelists considered a task ‘highly recommended’ or ‘desirable’ and if no opposing arguments were provided. These tasks will be included in the guideline. Tasks that at least 50% of the panelists considered ‘not relevant’ will be excluded from the guideline. Tasks that were indeterminate will be taken to the second round. All responses of the first round are currently being aggregated and will be fed back to panelists in the second round. A third round will only be performed if the results of the second round require it.


Since the Delphi method allows a large group of international experts to participate, we consider it to be the preferred consensus-based method for our study. Based upon this consultation process, a guideline will be developed on instrument selection for outcomes to be included in a COS.

COMET; Core outcome set; Delphi study; Outcome measurement instruments; Selection; Protocol; Guideline