In association with

  • Bristol, North Somerset and South Gloucestershire Clinical Commissioning Group Research and Evidence Team
  • West of England Academic Health Science Network



p value

The probability that a particular result would have happened by chance.


A placebo is a fake or inactive intervention, received by the participants allocated to the control group in a clinical trial. It is indistinguishable from the active intervention received by patients in the experimental group. One definition is that use of a placebo describes what happens when you do nothing, so that in the context of a clinical trial, for instance, a placebo group could describe the natural history of a disorder without the intervention under test. It is the effect we see when we do nothing.

Positive predictive value (+PV)

The proportion of people with a positive test who have disease.


This employs objectivity and is characterised by single truths; observation; measurable features and utilises quantitative methodologies. Its language is that of numbers.

Post-marketing surveillance

A procedure implemented after a drug has been licensed for public use, designed to provide information on the actual use of the drug for a given indication, and on the occurrence of side effects and adverse reactions. It’s a method for epidemiologic study of adverse drug reactions.

Post-test probability

The probability that a patient has the disorder of interest after the test result is known.

Pre-test probability

The probability that a patient has the disorder of interest prior to administering a test.


The baseline risk of a disorder in the population of interest.


Prevention refers to measures taken by an individual or a society to prevent disease happening or its consequences. In general, prevention includes a wide range of interventions, aimed at reducing risks to health. These are grouped into three categories:

  1. Primary prevention: refers to strategies used to prevent a disease happening in the first place. An example may be salt reduction to prevent an individual becoming hypertensive. Medication can be used in primary prevention such as the use of blood lowering or cholesterol lowering drugs to lower the risk of a stroke or heart attack.
  2. Secondary prevention: refers to strategies used in those with an existing disease which prevent recurrence, or significant morbidity. For example, in someone who has a heart attack cholesterol lowering drugs are used to lower the risk of subsequent heart attack and death.
  3. Tertiary prevention: refers to the prevention of long term chronic disease progression, physical deterioration and attendant suffering. For example, removing allergens which may aggravate asthmatic patients; screening for eye, renal, eye, and foot problems among diabetics to reduce the risks of complications.


The prospect of survival and recovery from a disease as anticipated from the usual course of that disease, or indicated by special features of the case.

Prognostic cohort study

This was in the CEBM glossary without anything against it

PsycINFO (Psychology Abstracts)

The PsycINFO (Psychology Abstracts) database provides extensive international coverage of literature on psychology and allied fields. PsycINFO covers psychological practice and research as well as the related clinical, social and biological disciplines. This includes information on drug and behavioural therapy, treatment of disease, drug addiction, developmental psychology, and educational psychology, as well as the psychological aspects of such areas as linguistics, social processes, pharmacology, physiology, nursing, education, anthropology, business and law. Covers the years 1806 to present and is updated weekly.

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