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Glossary of terms

Observational study In research, this refers to a study in which nature is allowed to take its course
and the investigator simply observes what is happening. Also known as a non-
experimental study. Changes or differences in one characteristic (e.g. whether or
not people received a specific treatment or intervention) are studied in relation
to changes or differences in other(s) (e.g. whether or not they died), without the
intervention of the investigator. There is a greater risk of selection bias than in
experimental studies. There are various types of observational studies, such as
cohort study, case–control study, cross-sectional study and case series.
Odds Odds are a way of representing probability, especially familiar for betting. It is
calculated by dividing the number of people with a defined outcome or event in
a given sample of population with the number of people who did not have that
outcome or event.
Odds ratio (OR) The ratio of the odds of an outcome in one group of people to the odds in
another group of people. In recent years odds ratios have become widely used in
reports of clinical studies. They provide an estimate (usually with a confidence
interval) for the effect of a treatment. An odds ratio of 1 between two treatment
groups for a specific outcome would imply that the risk of that outcome is the
same in each group. For rare events the odds ratio and the relative risk (which
uses actual risks and not odds) will be very similar. See also relative risk or risk
ratio (RR).
Oral rehydration salt (ORS) Specially constituted fluid containing as essential ingredients an organic solute (e.g.
solution a carbohydrate or amino acid) and sodium chloride. Such organic solutes
are subject to active intestinal co-transport (absorption) with sodium and so
enhance salt and hence water absorption. Most ORS solutions contain glucose
as the organic solute.
Oral rehydration therapy The administration of fluids by mouth or via nasogastric tube.
(ORT)
Osmolarity Osmotic concentration.
Osmosis The movement of solvent molecules across a membrane to an area where there
is a higher concentration of solute to which the membrane is impermeable.
Outcome The end result of care and treatment and/ or rehabilitation. In other words, the
change in health, functional ability, symptoms or situation of a person, which
can be used to measure the effectiveness of care/treatment/rehabilitation.
Researchers should decide what outcomes to measure before a study begins;
outcomes are then assessed at the end of the study.
Paralytic ileus A functional obstruction of the ileum (bowel) due to loss of intestinal movement.
Parasite An organism that obtains food and shelter from another organism.
PCT See primary care trust.
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.
Phlebitis Inflammation of a vein.
Photophobia An abnormal intolerance to light.
Placebo Placebos are fake or inactive treatments received by participants allocated to
the control group in a clinical trial and which 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.
Point estimate The best single estimate for the true value of a treatment effect or other
measurement obtained from a research study. For example, researchers in one
clinical trial take their results as their best estimate of the real treatment effect for
the population from which the study sample was selected – this is their estimate
at their point in time. The precision or accuracy of the estimate is measured by
a confidence interval.

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