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Glossary of terms

Coeliac disease A condition in which the small intestine absorptive surface is damaged owing
to an intolerance to gluten. It may lead to impaired digestion and absorption of
foods and may be associated with diarrhoea.
Cohort A group of people sharing some common characteristic or exposure (e.g. people
working in a specific environment or patients with the same disease) within a
specified period of time.
Cohort study A type of observational study that takes a group (cohort) of people and follows
their progress over time in order to measure outcomes such as disease or mortality
rates and make comparisons according to the type of exposure (treatments or
interventions) that they received. For example, comparing mortality between
one group of patients that received a specific treatment and one group which did
not (or between two groups that received different levels of treatment). Cohorts
can be assembled in the present and followed into the future (a ‘concurrent’ or
‘prospective’ cohort study) or identified from past records and followed forward
from that time up to the present (a ‘historical’ or ‘retrospective’ cohort study).
Colloid fluids Substances that do not dissolve into a true solution and do not pass through a
semi-permeable membrane. Colloid solutions tend to remain in the intravascular
compartment (within the circulation) longer than crystalloid solutions, and so a
smaller amount may be needed to maintain an adequate intravascular volume.
Colloids also increase colloidal osmotic pressure, and so draw water from the
interstitial spaces into the intravascular compartment. However, when capillary
permeability is increased, colloids may leak across the capillary membrane and
increase interstitial oncotic pressure, causing oedema. This may also happen
if too much colloid is given. Types of colloids include dextran and gelatin (e.g.
Gelofusine® and Haemaccel®).
Confidence interval (CI) A statistical technique used to express uncertainty about the findings from a
study or group of studies. A confidence interval describes a range of possible
effects (of a treatment or intervention) that are consistent with the results of a
study or group of studies. A wide confidence interval indicates a lack of certainty
or precision about the true size of the clinical effect and is seen in studies with
too few patients. Where confidence intervals are narrow they indicate more
precise estimates of effects and a larger sample of patients studied. It is usual to
interpret a ‘95%’ confidence interval as the range of effects within which we are
95% confident that the true effect lies.
Concealment of allocation The process of ensuring that the researcher entering new participants in a random-
or allocation concealment ised controlled trial is unaware of the group (intervention or control) the
participants have been allocated/assigned to. This is distinct from blinding and
is done to prevent selection bias.
Confounder or confounding A factor or a variable that can distort the true relationship between the exposure/risk
factor/variable factor and outcome in a study and can contribute to misleading findings if it
is not understood or appropriately dealt with. It is an important cause of bias
in study results and can be dealt with during the stage of study design or data
analysis or both. For example, if a group of people exercising regularly and a
group of people who do not exercise have an important age difference then
any difference found in outcomes about heart disease could well be due to one
group being older than the other rather than due to the exercising. Age is the
confounding factor here and the effect of exercising on heart disease cannot be
assessed without adjusting for age differences in some way.
Consensus methods A variety of techniques that aim to reach an agreement on a particular issue. In
the development of clinical guidelines, consensus methods may be used where
there is a lack of strong research evidence on a particular topic.
Constipation A condition in which passing faeces occurs infrequently, or with difficulty.
Control group In a controlled trial it refers to a group of participants recruited to act as a
comparator for one or more healthcare intervention. This group may receive
no healthcare intervention, continue standard treatment or receive a placebo
(dummy treatment) in order to provide a comparison for a group receiving an
experimental intervention , such as a new drug. It is also known as a comparison
group.

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