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Glossary of terms

Specificity In diagnostic testing, this refers to the proportion of cases without the target
condition correctly identified by the diagnostic test out of all the cases that do
not have the target condition.
Standard deviation (SD) A measure of the spread, scatter or dispersion of a set of measurements. Usually
used along with the mean (average) to describe numerical data.
Standardised mean The difference in the means divided by a standard deviation. This standard
difference (SMD) deviation is the pooled standard deviation of participants’ outcomes across
the whole trial. An important differerence from the weighted mean difference
(WMD) is that the value of the SMD is not dependent on the measurement scale
or unit, for example different trials may be assessing the same outcome (such
as weight) but using different scales/units for measuring it (such as kilograms or
ounces).
Statistical power or power The ability of a study to demonstrate a statistically significant result (association
or difference between two variables) given that such a result exists in the
population from which the sample was recruited. For example, 80% power in
a clinical trial means that the study has an 80% chance of ending up with a
P value of less than 5% in a statistical test (i.e. a statistically significant treatment
effect) if there really was an important difference (e.g. 10% versus 5% mortality)
between treatments. If the statistical power of a study is low, the study results will
be questionable (the study might have been too small to detect any differences).
By convention, 80% is an acceptable level of power. See also P value.
Structured interview A research technique where the interviewer controls the interview by adhering
strictly to a questionnaire or interview schedule with pre-set questions.
Study checklist A list of questions addressing the key aspects of the research methodology that
must be in place if a study is to be accepted as valid. A different checklist is
required for each study type. These checklists are used to ensure a degree of
consistency in the way that studies are evaluated.
Study population People who have been identified as the subjects of a study.
Study quality See methodological quality.
Study type The kind of design used for a study. Randomised controlled trial, case–control
study and cohort study are all examples of study types.
Subject A person who takes part in an experiment or research study.
Survey A study in which information is systematically collected from people (usually
from a sample within a defined population).
Systematic error See bias.
Systematic review A study with a clearly formulated question that uses systematic and explicit
methods with predetermined criteria to identify, appraise and synthesise the
results of relevant research. It may or may not include a meta-analysis to
summarise the results.
Systemic Involving the whole body.
Tachycardia An abnormally rapid heart rate.
Tachypnoea An abnormally rapid breathing rate.
Target population The people to whom guideline recommendations are intended to apply.
Recommendations may be less valid if applied to a population with different
characteristics from the participants in the research study, for example in terms
of age, disease state or social background.
Tertiary centre A major medical centre providing complex treatments that receives referrals
from both primary and secondary care. Sometimes called a tertiary referral
centre. See also primary care and secondary care.
Toxic shock syndrome A state of acute shock, due to septicaemia, that can be life-threatening if not
treated.
Triple-blind study A study in which the statistical analysis is carried out without knowing which
treatment patients received, in addition to the patients and investigators/
clinicians being unaware which treatment patients were getting.

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