Here is a glossary of common terms used within healthcare research trials

Research glossary

Arm

A group of patients receiving a particular treatment (or placebo) in a clinical trial.

Blind

Trials where a new treatment is compared against another treatment or a placebo (usually phase III trials). A trial is ‘single-blind’ if either the participants or the researchers do not know which option the participants are receiving, and ‘double-blind’ if both the participants and the researchers do not know which option the participants are receiving. This makes the results of the trial more objective and therefore more reliable.

Cohort

A group of individuals with some characteristics in common, e.g. a group of people born within the same period would be referred to as a birth cohort.

Contraindication

A specific circumstance when the use of a treatment could be harmful, e.g. aspirin allergy is a contraindication to taking aspirin.

Control/control group

An alternative to a new treatment that is used as a comparison. Controls are usually either an existing treatment, a placebo or no treatment.

Crossover trial

A trial that involves patients receiving one treatment for a certain amount of time, then swapping to an alternative treatment for another period of time.

Double-blind

See ‘blind’.

Eligibility criteria

A detailed description of the patients or volunteers who can or cannot take part in a trial.

Informed consent

The process of learning what is involved in a clinical trial and then agreeing to take part.

Longitudinal study

A study that follows a group of patients over a period of time.

Meta-analysis

A review of the results of a large number of trials on a similar subject. A meta-analysis can be a particularly powerful research tool.

Multi-centre trial

A trial being carried out at more than one location.

Observational study

A study where the researcher is not directly controlling the experiment but instead is simply observing behaviour or outcomes. No attempt is made to affect the outcome, e.g. no treatment is given.

Peer review

A review of a trial’s results by a group of independent experts

Phase I trial

Phase II trial

Phase III trial 

Placebo

A ‘dummy’ treatment that resembles a medical treatment but is intended to have no physical effect on a participant. A new treatment is often compared against a placebo to get more reliable evidence about its effectiveness. Patients who receive a placebo will still also receive the best standard care.

Prospective study

Research in which a group of participants is identified, and then studied from that point forward in time. The opposite is a retrospective study.

Randomised trial

Participants are allocated to receive one type of treatment or another by a random, automated process. This helps ensure the results are objective and unbiased.

Retrospective study

Research in which a group of participants is identified, and then studied from that point backwards in time, usually via their medical records and interviews. The opposite is a prospective study.

Single-blind

See ‘blind’.