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What are core outcomes?

To help patients, doctors and other health professionals make decisions about treatments, we need evidence about what works best. Treatments are developed and tested by researchers to make sure they work and are safe. To do this researchers need to look at the effects those treatments have on patients. Researchers do this by measuring an ‘outcome’.

For example, in a study of how well a new adenomyosis treatment works, ‘outcomes’ might include:

  • A measure of how many days the menstrual period lasts

  • Pain during the menstrual period

  • Quality of life

It is important that researchers choose outcomes that are relevant to the people who will receive the treatment that is tested. For example, it might not be important to a woman how a drug changes the blood flow through the womb, but she might be interested in how it improves her symptoms. 


Image by Sixteen Miles Out

Research studies often assess how effective particular medical treatments are, but the results can be different between studies. Therefore it is important to group the results from individual studies together into a larger study called a meta-analysis, that aims to give us a more definitive idea about whether treatment is effective or not.


Meta-analyses are only useful when they are comparing similar outcomes and unfortunately, the outcomes used by research studies are often highly variable. A recent example is that researchers tried to look into how the technology HIFU improved heavy bleeding in women with adenomyosis. Despite there being more than 16 studies on the topic, it was not possible to calculate the effect of this treatment on heavy menstrual bleeding. This was because not all studies reported the outcome "heavy menstrual bleeding" and those who did, measured it in different ways.

Another problem is when a study team sets out to collect information on several outcomes but in the end, only publishes the results of some of the outcomes. This sometimes happens when the findings for particular outcomes differ from those the team hoped for.

The aim of a core outcome set is to agree and standardise what the most important outcomes should be for a particular condition. This core outcome set should be measured and reported in all studies. This guarantees that the research is useful, patient-centred and the outcomes can be compared more easily.

A core outcome set is only the minimum of what should be measured, researchers can add more outcomes to their projects, if they want.


The core outcomes are agreed upon by groups of healthcare professionals, patients and researchers with the hope that they will be widely used in future research studies. The ultimate aim is to make research conclusions easier to draw and more relevant to key stakeholders including patients.

Image by Marc-Olivier Jodoin
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