The NICE glossary provides brief definitions and explanations of terms and jargon used on our site. The terms describe how we work and how our guidance is produced.

Our glossary excludes specific clinical and medical terms although we intend to include these in the longer term. If you cannot find the term you are looking for, please email us so that we can consider adding it to the glossary. New terms are added regularly.

The glossary is not used for indexing the site or for navigation - for information on this, please see the NICE taxonomy.

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 model

A way to estimate the costs and effects of a technology or treatment over periods of time on patient groups not covered in a clinical trial or other research.


Experimental Event Rate - see Event rate.

Effect size

A measure that shows the magnitude of the outcome in one group compared with that in a control group.

For example, if the absolute risk reduction is shown to be 5% and it is the outcome of interest, the effect size is 5%.

The effect size is usually tested, using statistics, to find out how likely it is that the effect is a result of the treatment and has not just happened by chance (that is, to see if it is statistically significant).


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


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.

Elective procedure

Non-urgent clinical procedures. For example surgery (such as a hip replacement) that has been planned in advance rather than done as an emergency.

Empirical evidence

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


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.


Equality involves recognising that everyone should be given access to the same opportunities, irrespective of their age, religion, class, ethnicity, sexuality or gender.


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 Review Group

A group of researchers that reviews the manufacturer's submission about a drug or other treatment, and produces a report for the Appraisal Committee. This happens for single technology appraisals only. In multiple technology appraisals, an assessment group produces an assessment report.

Evidence statement

A brief summary of one finding from a review of evidence that a clinical guideline or piece of public health guidance is based on.

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' decisions or recommendations are based on research findings that have been systematically appraised - that is, the best available evidence.

Evidence-based clinical 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).

Exclusion criteria

See selection criteria.

Executive Lead

The NICE executive director who is responsible for a piece of guidance. Executive leads are not usually involved day to day in the production of guidance.

Experimental event rate

See event rate.

Experimental study

A study in which the people taking part are sorted into two or more groups. At least one 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 studies (rather than observational studies) are the best choice for medical studies because they use control groups and minimise bias. See non-experimental study and quasi-experimental study.

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.

Expert adviser

A person who has specialist knowledge in a particular area related to a clinical guideline. The expert adviser attends meetings of the guideline development group to give advice, but is not a full member of the group.

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. See also validity.


An assumption that the results of studies of a specific population will also hold true for another population with similar characteristics.

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This page was last updated: 15 April 2011

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Selected, reliable information for health and social care in one place

Accessibility | Cymraeg | Freedom of information | Vision Impaired | Contact Us | Glossary | Data protection | Copyright | Disclaimer | Terms and conditions

Copyright 2014 National Institute for Health and Care Excellence. All rights reserved.