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.

  • Economic evaluation

    An economic evaluation is used to assess the cost effectiveness of healthcare interventions (that is, to compare the costs and benefits of a healthcare intervention to assess whether it is worth doing). The aim of an economic evaluation is to maximise the level of benefits - health effects - relative to the resources available. It should be used to inform and support the decision-making process; it is not supposed to replace the judgement of healthcare professionals.
    There are several types of economic evaluation: cost-benefit analysis, cost-consequence analysis, cost-effectiveness analysis, cost-minimisation analysis and cost-utility analysis. They use similar methods to define and evaluate costs, but differ in the way they estimate the benefits of a particular drug, programme or intervention.
  • Economic modelling

    A way to estimate the costs and effects of an intervention over periods of time on patient groups not covered in a clinical trial or other research.
  • Effect size

    The observed association between interventions and outcomes, or a statistic to summarise the strength of the observed association.
  • Effectiveness

    How beneficial a test or treatment is under usual or everyday conditions, compared with doing nothing or opting for another type of care.
  • Efficacy

    How beneficial a test, treatment or public health intervention is under ideal conditions (for example, in a laboratory), compared with doing nothing or opting for another type of care.
  • Empirical evidence

    Evidence that is based on experience (observation or an experiment) rather than on reasoning alone.
  • Epidemiology

    The study of the causes, distribution, control and prevention of disease. Epidemiologists collect and examine medical data and spot health trends to establish which diseases are on the increase and where, which treatments and other activities work and which do not. (This includes activities to prevent disease and to improve health and wellbeing.) In other words, they consider the possible risk factors for a whole population or area, not just for individual patients.
  • Evaluation

    An assessment of an intervention (for example, a treatment, service, project, or programme) to see whether it achieves its aims.
  • Event rate

    The proportion of patients in a group who have a specific experience (for example, whose symptoms become less severe). This could also be described as a result or event. If 27 out of 100 patients have the experience, the event rate is 0.27 or 27%. The terms 'control event rate' and 'experimental event rate' may be used to describe control and experimental groups of patients respectively.
  • Evidence

    Information on which a decision or guidance is based. Evidence is obtained from a range of sources, including randomised controlled trials, observational studies and expert opinion (of healthcare and other professionals and/or patients).
  • Evidence Review Group

    For single technology appraisals. a group of researchers that reviews the manufacturer's submission about a drug or other treatment, carries out exploratory analyses using the manufacturer's economic model, and produces a report for the Appraisal Committee.
  • Evidence statement

    A brief summary of the key findings from a review of evidence that has been used as the basis for a recommendation in a guideline.
  • Evidence summaries: new medicines

    Quality-assured summaries of the best available evidence for new medicines, or existing medicines with new indications or a new formulation. They help commissioners, budget holders and groups such as Area Prescribing Committees make informed decisions and aid local planning on the introduction of key new medicines.
  • Evidence summaries: unlicensed and off-label medicines

    Quality-assured summaries of the best available evidence for selected unlicensed and off-label medicines. They allow evidence-based prioritisation, treatment and funding decisions to be made in cases where there are no clinically appropriate licensed alternatives.
  • Evidence table

    A table summarising the results of studies that, taken together, provide the evidence to support a particular recommendation or series of recommendations in NICE guidance.
  • Evidence-based practice

    Decisions about patient care based on the best research evidence available, rather than on personal opinions or common practice (which may not always be evidence-based).
  • Executive Lead

    The NICE executive director who advises on a specific piece of guidance. Executive leads are not usually involved on a day-to-day basis in the production of guidance but are called on as needed at different stages of guidance development.
  • Experimental study

    A study in which the people taking part are sorted into 2 or more groups. At least 1 will be a control group. All groups are then followed up under carefully controlled conditions to investigate whether or not a test or treatment affects the course or outcome of a condition or disease. A controlled clinical trial and randomised controlled trial are examples of experimental studies.
  • Experimental treatment

    A new treatment (for example, a new drug) that is being studied to see whether it has an effect on the course or outcome of a condition or disease.
  • External validity

    The degree to which the results of a study hold true in non-study situations, for example in routine NHS practice. May also be referred to as the generalisability of study results to non-study populations. For example, the external validity of the study that took place in Spain may be questioned if the population the results were applied to was people in Australia.
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