In association with

  • Bristol, North Somerset and South Gloucestershire Integrated Care Board
  • West of England Academic Health Science NetworkWest
  • National Institute for Health Research



n-of-1 trial

A variation of a randomised controlled trial in which a sequence of alternative treatment regimens is randomly allocated to a patient. The outcomes of regimens are compared, with the aim of deciding on the optimum regimen for the patient.

Natural Experiments

“work best in circumstances where a relatively large population is affected by a substantial change in a well-understood environmental exposure, and where exposures and outcomes can be captured through routine data sources, such as environmental monitoring and mortality records”

MRC (2006) Developing and evaluating complex interventions: new guidance

Negative predictive value (-PV)

The proportion of people with a negative test who are free of disease.

Nested case-control study

A case control study in which cases and controls are drawn from the population in a cohort study. As some data is already available about both cases and controls, the effects of some potential confounding variables are reduced or eliminated. In this type of case-control study, a set of controls is selected from subjects i.e. non-cases at risk at the time of occurrence of each case that arises in a cohort, thus allowing for the confounding effect of time in the analysis.

NICE Guidelines

NICE Guidelines National Institute for Health and Care Excellence publishes a table of clinical guidelines.  Guidance sets the standards for high quality healthcare and encourages healthy living.  NICE guidance can be used by the NHS, Local Authorities, employers, voluntary groups and anyone else involved in delivering care or promoting wellbeing.  This is available as a free app for mobile devices

Nuffield Trust

Nuffield Trust is an authoritative and independent source of evidence-based research and policy analysis for improving health care in the UK

Number needed to treat (NNT)

The number of patients who need to be treated to prevent one bad outcome. It is the inverse of the ARR: NNT=1/ARR. Numbers needed to harm (NNH) is the number of patients who, if they received the experimental treatment, would lead to one additional person being harmed compared with patients who receive the control treatment. It is calculated as 1/ARI.

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