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What is a Core Outcome Set?

" To help patients, doctors and other healthcare professional 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 these treatments have on patients. Researchers do this by measuring an outcome. "

For example, in a study of how well a new Caesarean scar ectopic pregnancy treatment works, 'outcomes' might include:

1. Total blood loss

2. Need for blood transfusion

3. Impact on psychological well being

If all studies in Caesarean scar ectopic pregnancy used the same outcomes, this would allow us to compare and combine outcomes.

At the moment, different studies looking at treatments for Caesarean scar ectopic pregnancy often measure different outcomes.

For example, imagine two new studies of how well a new treatment for Caesarean scar ectopic pregnancy works.

1. Study 1 - researchers measure blood loss as an outcome

2. Study 2 - researchers measure need for further treatment as an outcome

When these two new studies are finished, we cannot compare or combine their results to assess how effective the treatment is, as they are not comparing like with like.

Another problem is when researchers set out to collect information on several outcomes but in the end only publish 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 on what the most important outcomes should be. These outcomes should then be reported in all studies.

A core outcome set is only the minimum of what should be measured and researchers can measure additional outcomes if they feel they are important in their particular study.