The NICE Glossary provides brief definitions and explanations of terms used on our site. The terms describe how we work and how our guidance is produced.
Our glossary excludes specific clinical and medical terms. If you cannot find the term you are looking for, please email us so that we can consider adding it to the glossary.
Some definitions and examples are based on those in the 'HTAi consumer and patient glossary', with thanks to Health Technology Assessment International.
The likelihood of an event or outcome occurring (for example, an adverse reaction to the drug being tested) among the group being studied. Studies that compare 2 or more groups of people may report results in terms of the absolute risk reduction.
A reduction in the likelihood of an event or outcome occurring as a result of a treatment or another intervention. For example, if a treatment reduces the absolute risk of death from 0.25 (25%) to 0.10 (10%), the absolute risk reduction (ARR) is 0.15 (15%), that is, 0.25 minus 0.10.
The estimate of absolute risk reduction often comes from clinical trials. The percentage of people taking part who are receiving treatment (treatment group) and experience a specific outcome is compared with the percentage of people taking part but not receiving treatment (control group) who experience the same outcome.