In a clinical trial, outcomes may assess endpoints in important functional areas, like safety and effectiveness.  Specific outcomes are chosen for measurement based on investigator preference, and these may include primary outcomes, which are the key measures for the study, as well as secondary outcomes. 

To minimize waste in research while ensuring that the best information is obtained for medical decision-making, it is desirable that the results of trials assessing similar interventions be able to be combined or compared.  A simple way to facilitate this is by encouraging investigators to use a basket of common outcome measures when studying the same disease or condition.  Core outcome sets are thus an agreed upon group of outcomes that are relevant to study of a particular condition.  The measures associated with each core outcome are called core outcome measures, and these are also agreed upon. 

Core outcomes emerge from a consensus of patients and healthcare professionals.  Additionally, other stakeholders, including scientists, regulators, representatives of patient support groups, journal editors, industry representatives, and payers may also be involved in the development process.  Since core outcome sets are intended to be used in many studies, they should be easy to administer.  Core outcome measures may be validated, widely accepted instruments.

Investigators who incorporate core outcome measures in their research are not dissuaded from selecting additional outcomes and measures that they deem appropriate.  Core outcome sets are intended to be a minimum basic set of relevant outcomes, rather than an exhaustive listing.