Core Outcome Sets (COS)

What is a Core Outcome Set (COS)?[1]

A Core Outcome Set (COS) is a minimum agreed upon standardized set of Patient Reported Outcomes (PROs) with a corresponding set of Patient Reported Outcome Measures (PROMs). PROs, or domains, identify what aspects of a health condition or disease should be measured in all scientific studies. PROMs within a COS are the measurement tools (often patient questionnaires) that are recommended for measuring the identified PROs (domains) in scientific studies. The development of a COS for health conditions involves an in-depth and collaborative process. When a set of PROs and PROMs have been agreed upon for a given health condition, this is referred to as a “core outcome set.” Even when a COS exists, researchers may choose to measure any additional outcomes relevant to the research (see image below).[2] It is important that a COS not contain too many outcomes so that individual researchers maintain the flexibility to adopt the COS alongside other domains they may want to study and measure.

In recent years, there has been an attempt within the pain management field to harmonize outcome assessment and provide guidance to develop COS. A COS should represent the pain domains (PROs) that are relevant to all stakeholders. Stakeholders can include patients, researchers/clinicians, caregivers, payors, Health Technology Assessment (HTA) experts, and any health professionals who have experience with the health condition. When developing a COS, stakeholders must first reach a consensus on the PROs (such as pain severity) to be measured for a disease or health condition. Once there is a consensus on the domains, the second step is to identify and define the patient-reported outcome measures (PROMs) that are best suited for assessing these domains. At the end of the consensus process, there will be a COS of PROs and PROMs that should be measured and reported in all clinical trials, clinical studies, and/or in clinical practice for a specific pain condition.

Why are COS important?

Core Outcome Sets are beneficial because they allow researchers to conduct systematic reviews and meta-analyses for specific health conditions. They do this by providing consistency on outcome assessments for aspects of the health condition, which allow results to be combined and compared. If all studies for a specific health condition measured the same outcomes, then the results of those studies could all be compared and combined for analytical purposes. COS are important for pain research because they could lead to more routine measurement of biopsychosocial data. A biopsychosocial approach better encompasses how individual patients experience pain and how different therapies affect the whole spectrum of pain-related effects.[3]

If patient representatives are involved in the consensus on a COS, the resulting COS would better reflect patients’ needs. Within the pain field this approach is of utmost need, as pain is a subjective experience with multi-facetted symptoms and signs.

Why should we develop COS for acute pain, chronic pain, the transition from acute to chronic pain, and episodic/breakthrough pain?

The need for COS has been widely accepted within the pain field, and this consensus has led to a number of initiatives that have developed COS for certain pain conditions. However, despite some overlaps (such as the recommendation to measure pain intensity as an outcome domain in almost every COS), other pain-related COS vary considerably in their chosen PROs and PROMS. In addition, pain is understood as a biopsychosocial phenomenon, but psychological aspects are underrepresented in many pain COS, and patient involvement in defining what is important (and how to measure it) has been inconsistently considered.[4]

Another issue that arises from disjointed sets of COS for pain is that research initiatives frequently revise the COS for their pain conditions, which makes comparability across pain conditions and across time difficult. Without overarching pain COS, the pain field suffers because different studies often use different outcomes to assess the efficacy of pain treatments, as well as different measurement tools – this limits the amount of comparability between studies.

Given the variation in COS that have been developed for pain conditions in recent years, it would be very valuable to develop four overarching COS – one for acute pain, one for chronic pain, one for the transition from acute to chronic pain, and one for episodic/breakthrough pain. One of the greatest benefits would be the opportunity for pain researchers to gain information and understanding about the most effective treatments for acute, chronic, the transition from acute to chronic, and episodic/breakthrough pain, which could lead to the adoption of better treatments for patients around the world who suffer from pain and pain-related conditions.

How and why are the NIH and IMI-PainCare working together to establish a COS?

Before INTEGRATE-Pain was established, both the NIH and IMI-PainCare were separately developing COS for researchers to use in pain-related clinical trials. Both sides realized that an opportunity existed for the international pain community to have access to high quality and meaningful data across pain conditions, in diverse populations, and across multiple interventions. Development of overarching COS for acute pain, chronic pain, the transition from acute to chronic pain, and episodic/breakthrough pain could make research in the field of pain even more patient-centered and relevant to patients than it is today.

As part of the groundwork to establish a COS, the INTEGRATE-Pain Consortium is conducting a systematic review of published scientific literature to identify pain-related COS initiatives around the world. As a result of the systematic literature review, INTEGRATE-Pain will bring together the identified COS initiatives, as well as and patient representatives, at a virtual meeting to discuss the results of the literature review and determine whether there is a need to develop overarching COS for acute, chronic, the transition from acute to chronic, and episodic/breakthrough pain. If participants identify the need for COS, then INTEGRATE-Pain will lead a consensus process (known as the Delphi Process) with the pain COS initiatives and meeting participants. During this process, voting participants will rank PROs and PROMs to create agreed-upon COS for acute, chronic, the transition from acute to chronic, and episodic/breakthrough pain for recommended use in clinical trials, clinical studies, and clinical practice.


  1. COMET Initiative. Involving Patient and the Public in Improving Research. Accessed January 14, 2022.
  2. Ibid.
  3. Pogatzki-Zahn E, Schnabel K, Kasier U. Patient-reported outcome measure for acute and chronic pain: current knowledge and future directions. Curr Opin Anaesthesiol. 2019 Oct;32(5):616-622.
  4. Ibid.
  5. Global People Diversity stock photo. Accessed January 14, 2022.