The NICE glossary provides brief definitions and explanations of terms used on the website. The terms describe how NICE works and how its 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.

For terms used in social care, the Care and Support Jargon Buster from Think Local Act Personal is a useful guide to the most commonly used social care words and phrases, and what they mean.

  • Absolute risk

    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.

  • Absolute risk increase

    An increase in the likelihood of an event or outcome occurring as a result of a treatment or another intervention, sometimes called the risk difference. It is broadly the same as the absolute risk reduction but occurs in the opposite direction. For example, if a treatment increased the absolute risk of major haemorrhage from 0.10 (10%) to 0.25 (25%), the absolute risk increase (ARI) is 0.15 (15%), that is, 0.25 minus 0.10 (25% minus 10%). The ARI is related to the number needed to harm.

  • Absolute risk reduction

    A reduction in the likelihood of an event or outcome occurring as a result of a treatment or another intervention, sometimes called the risk difference. 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  (25% minus 10%). The estimate of ARR often comes from clinical trials. The percentage of people taking part who are having treatment (treatment group) and experience a specific outcome is compared with the percentage of people taking part but not having treatment (control group) who experience the same outcome. The ARR is related to the number needed to treat.

  • Abstract

    A summary of a study, which may be published alone or as an introduction to a full scientific paper.

  • Active monitoring

    Active monitoring is ongoing surveillance in key topic areas. It involves 1 or more of:

    • monitoring studies in progress by systematically searching for ongoing studies and assessing the results when published
    • monitoring newly published studies by continuous searching of newly published evidence
    • system monitoring by systematically collating intelligence from the health and care system, and working with partners to identify areas of change.
  • Acute sector

    Hospital-based healthcare services for inpatients, outpatients and people having day-case treatments.
  • Adherence

    The extent to which someone follows the health advice agreed with healthcare professionals. Sometimes referred to as 'compliance'.

  • Adverse effect

    An unintended effect that is harmful or otherwise unwanted, and suspected to be related to, or caused by, a drug, treatment or intervention. See also Side effect.

  • Adverse event

    Any undesirable event experienced by a person while they are having a drug or any other treatment or intervention, regardless of whether or not the event is suspected to be related to or caused by the drug, treatment or intervention.

  • Adverse reaction

    An unintended reaction that is harmful or otherwise unwanted which is experienced by a person after having a drug or any other treatment or intervention, and which is suspected to be related to, or caused by the drug, treatment or intervention.


    An international collaboration of researchers and policy makers, the aim of AGREE (appraisal of guidelines research and evaluation) is to improve the quality and effectiveness of practice guidelines. The AGREE II instrument, developed by the group, is designed to assess the quality of clinical guidelines.

  • AI and Digital Regulations Service

    This is a multi-agency collaboration between 4 organisations that supports the development and widespread adoption of safe, innovative, value-adding technologies in health and social care. It provides guidance to support developers and adopters of AI and digital technologies across the regulatory, evaluation and data governance pathways. The 4 organisations are NICE, the Medicines and Healthcare products Regulatory Agency, the Health Research Authority and the Care Quality Commission.

  • Allocation concealment

    The process used to prevent (conceal) advance knowledge of what intervention group people have been assigned to in a randomised controlled trial. It should be done by someone who is not responsible for recruiting people into the trial. The process prevents researchers from (unconsciously or otherwise) influencing which people are assigned to a given intervention group. Allocation concealment is different from blinding or masking; a double blind study can have unconcealed allocation and an open-label (unblinded) study can have concealed allocation.

  • Analysis

    The process of looking for patterns in information to identify cause and effect or answer specific questions, such as whether a treatment or other intervention works and what the risks are.

    There are 2 types of analysis. Quantitative analysis looks for patterns in the form of numbers, such as most frequent choice of treatment option or average rating of pain during treatment. Qualitative analysis looks for patterns of meaning, feeling or beliefs. It can lead to a finding such as 'most people who support paying more for end-of-life therapy also believe society should give more to those with greater need'.

  • Appeals process

    The final part of the process for producing technology appraisal and highly specialised technology guidance. Organisations representing patients and carers, healthcare professionals and companies can appeal against final advice given by the independent evaluation committee on a specific medicine or treatment. The grounds for appeal are that NICE has failed to act fairly, or has exceeded its powers, or that a recommendation is unreasonable in light of the evidence submitted.

  • Applicability

    How well an observation or the results of a study or review are likely to hold true in a particular setting.

  • Appraisal of evidence

    Formal assessment of the quality of research evidence and its relevance to the topic being considered. It is assessed according to predetermined criteria.
  • Arm (of a clinical study)

    A subsection of people within a clinical study who have a particular intervention (for example, the 'usual care' arm).

  • Assessment group

    An independent group of researchers commissioned by NICE to review the evidence on a group of treatments, for a multiple technology appraisal. The assessment group includes researchers who assess the quality of studies on the treatments, and health economists who look at whether the treatments are good value for money. The evaluation committee bases its discussions on the assessment report produced by the assessment group.

  • Assessment report

    A review of the evidence about how well health technologies work and how much value for money they present. The assessment report forms the basis of the evaluation committee's discussions. The assessment report is written by an assessment group. Assessment reports are produced for treatments being assessed using the multiple technology appraisal process.

  • Audit

    A systematic review of a practice, process or performance to establish how well it meets predetermined criteria. The procedure includes identifying problems, developing solutions, making changes to practice, and then reviewing the whole operation or service again. For example, an audit may be carried out on a specific service (such as 'stop smoking' services), to check whether it complies with laws, regulations or policies. See also Clinical audit.

  • Audit committee

    A subcommittee of NICE's board that keeps a check on NICE's finances and other aspects of the way the organisation is run.

  • Audit trail

    Records of action to assess practice against standards. Also, a clear record of actions so that the reasons for the actions are apparent to a third party. For example, the reasons for changes to a draft guideline should be clearly recorded.