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.

  • Randomisation (random allocation)

    Assigning participants in a research study to different groups without taking any similarities or differences between them into account. For example, it could involve using a random numbers table or a computer-generated random sequence. It means that each individual (or each group in the case of cluster randomisation) has the same chance of receiving each intervention.
  • Randomised controlled trial

    A study in which a number of similar people are randomly assigned to 2 (or more) groups to test a specific drug or treatment. One group (the experimental group) receives the treatment being tested, the other (the comparison or control group) receives an alternative treatment, a dummy treatment (placebo) or no treatment at all. The groups are followed up to see how effective the experimental treatment was. Outcomes are measured at specific times and any difference in response between the groups is assessed statistically. This method is also used to reduce bias.
  • Relative risk

    The ratio of the risk of disease or death among those exposed to certain conditions compared with the risk for those who are not exposed to the same conditions (for example, the risk of people who smoke getting lung cancer compared with the risk for people who do not smoke).
    If both groups face the same level of risk, the relative risk is 1. If the first group had a relative risk of 2, subjects in that group would be twice as likely to have the event happen. A relative risk of less than 1 means the outcome is less likely in the first group. Relative risk is sometimes referred to as risk ratio.
  • Reliability

    The ability to get the same or similar result each time a study is repeated with a different population or group.
  • Remuneration Committee

    A subcommittee of NICE's Board that sets the salaries and terms of service for senior staff.
  • Research recommendation

    Recommendations for future research covering questions relating to an uncertainty or lack of evidence that has been identified while developing NICE guidance.
  • Resolution process

    Before interventional procedures, medical technology or diagnostics guidance is published, consultees can ask for a 'resolution' if they think that the guidance is inaccurate or the process for developing interventional procedures guidance has not been followed. During the resolution process any concerns raised by the consultees are investigated.
  • Retrospective study

    A research study that focuses on the past and present. The study examines past exposure to suspected risk factors for the disease or condition. Unlike prospective studies, it does not cover events that occur after the study group is selected.
  • Review date

    The date at which we plan to start a check to see if guidance needs to be updated. If this check finds a large amount of new evidence has been produced since the original guidance, we may propose that all or part of the guidance is updated.
  • Review of the literature

    A summary of the evidence in a number of different individual studies, with conclusions about their findings. A review may or may not be systematically researched and developed.
  • Review protocol

    A document that outlines the background, objectives and planned methods for a systematic review.
  • Risk Factor

    Any aspect of a person's lifestyle, environment or pre-existing health condition that may increase their risk of developing a specific disease or condition.
  • Risk Management Committee

    A subcommittee of NICE's board that advises staff on identifying risks to the organisation and how to reduce them. Its work includes making sure NICE follows legislation on issues such as health and safety and data protection, and advising on preventing errors in published guidance.
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