I’m developing a Core Outcome Set (COS)

You want to develop a Core Outcome Set for use in your field and subsequently select outcome measurement instruments for each core outcome.

The challenge is to deliver high quality COS that meet quality standards that are based on state of the art methodology for COS development and following new clinimetric developments. Guidance on what and how to measure has been established and can be found here.

What is a Core Outcome Set (COS)?

A COS is a consensus-based agreed minimum set of outcomes that should be measured and reported in all clinical trials of a specific disease or trial population; it is a recommendation of what should be measured and reported in all clinical trials. An outcome refers to what is being measured. It is also referred to as a construct or domain. In the context of a clinical trial it refers to what is being measured on trial participants to examine the effect of exposure to a health intervention.

Once the COS is defined, it is then important to achieve consensus on how these outcomes should be measured, i.e. which outcome measurement instruments should be selected. An outcome measurement instrument refers to how the outcome is being measured. It is a tool to measure a quality or quantity of the outcome. The tool can be a single question, a questionnaire, a score obtained through physical examination, a laboratory measurement, a score obtained through observation of an image, etcetera.

Resources to help you develop a COS:

1 COMET Handbook 1.0

COMET published the COMET Handbook version 1.0, which provides guidance on the development of COS (open access). Additionally, COMET is maintaining an international database for existing and ongoing work on core set development. COS developers are encouraged to register their COS project within this database.



In an EU (7th Framework) funded program, COSMIN collaborated with the COMET initiative and developed a guideline for the selection of outcome measurement instruments for outcomes included in a core set. In a 4-step process,  this guideline guides you through the process of defining how to measure the core outcomes that are included in the COS.


OMERACT Handbook and Filter 2.0

OMERACT has published ‘Filter 2.0’; a conceptual framework and process for the development of core outcome sets, and the OMERACT Handbook; a comprehensive overview of the OMERACT methodology on all different stages of the COS development process –from defining what to measure up to the involvement of patient research partners and OMERACT’s publication policy (available from http://www.omeract.org).


HOME roadmap

HOME has published a methodological framework to develop COS in dermatology: the HOME Roadmap.



Currently, the Standard Protocol items for studies developing core outcome sets (COS-STAP) project is developing a list of protocol items for core outcome set studies. The Delphi study is ongoing and more information will be announced upon publication of the study results.



The Core Outcome Set – Standards for Development (COS-STAD) project has developed 11 minimum standards that are recommend to be followed by COS developers in the development of their COS.



The Core Outcome Set – Standards for Reporting (COS-STAR) project has developed the Core Outcome Set-STAndards for Reporting (COS-STAR) Statement as a reporting guideline for COS studies. The COS-STAR Statement is a helpful resource to improve the reporting of COS studies for the benefit of all COS users.