A5V4d

Abbreviations and glossary
Peer review Review of a study, service or recommendations by those with similar interests
and expertise to the people who produced the study findings or
recommendations. Peer reviewers can include professional and/or patient/carer
representatives.
Performance bias Systematic differences in care provided apart from the intervention being
evaluated. For example, if study participants know they are in the control group
they may be more likely to use other forms of care, people who know they are
in the experimental group may experience placebo effects, and care providers
may treat patients differently according to what group they are in. Masking
(blinding) of both the recipients and providers of care is used to protect against
performance bias.
Pilot study A small scale ‘test’ of the research instrument. For example, testing out
(piloting) a new questionnaire with people who are similar to the population of
the study, in order to highlight any problems or areas of concern, which can
then be addressed before the full-scale study begins.
Placebo Placebos are fake or inactive treatments received by participants allocated to
the control group in a clinical trial that are indistinguishable from the active
treatments being given in the experimental group. They are used so that
participants are ignorant of their treatment allocation in order to be able to
quantify the effect of the experimental treatment over and above any placebo
effect due to receiving care or attention.
Placebo effect A beneficial (or adverse) effect produced by a placebo and not due to any
property of the placebo itself.
Point estimate A best single estimate (taken from research data) for the true value of a
treatment effect or other measurement. For example, researchers in one
clinical trial take their results as their best estimate of the real treatment effect –
this is their estimate at their point in time. The precision or accuracy of the
estimate is measured by a confidence interval. Another clinical trial of the same
treatment will produce a different point estimate of treatment effect.
Positive predictive value
(PPV)
Power See statistical power.
The proportion of people with a positive test result who have the disease
(where having the disease is indicated by the ‘gold’ standard test being
positive).
Primary care Health care delivered to patients outside hospitals. Primary care covers a
range of services provided by GPs, nurses and other healthcare professionals,
dentists, pharmacists and opticians.
Primary care trust (PCT) A primary care trust is an NHS organisation responsible for improving the
health of local people, developing services provided by local GPs and their
teams (called primary care) and making sure that other appropriate health
services are in place to meet local people’s needs.
Probability How likely an event is to occur, for example how likely a treatment or
intervention will alleviate a symptom.
Procalcitonin A precursor of the hormone calcitonin that is released into the bloodstream in
response to infection or inflammation. Proclacitonin can be measured in blood
samples and it is currently under development as a potential test for the
detection of serious infections.
Prognostic factor Patient or disease characteristics, for example age or co-morbidity, that
influence the course of the disease under study. In a randomised trial to
compare two treatments, chance imbalances in variables (prognostic factors)
that influence patient outcome are possible, especially if the size of the study is
fairly small. In terms of analysis these prognostic factors become confounding
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