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Glossary to Clinical Trial Terms

Glossary of Common Terms Used in Clinical Trials

The research community has its own language and when you take part in a clinical study you may encounter terms that you are not familiar with. Here is a list of the more commonly used ones.

Adverse Event – Any negative change in a study participant’s condition that occurs during the study or shortly afterwards that may or may not be related to the intervention being investigated.

Adverse Drug Reaction – An adverse event that is thought to be caused by the interventional medication being studied at doses that would normally be used for treatment.

Arm – Any of the groups of participants involved in a clinical study that may or may not be receiving the intervention being investigated.

Blinding – A strategy used in clinical studies where either the participants and/or the investigators don’t know which groups receive or don’t receive the intervention being studied. This is done in an effort to limit bias.

Control Group – A group of participants in the study that do not receive the intervention being investigated but are followed similarly in order to compare to the group receiving treatment. This group may instead receive a placebo or another intervention, which may or may not be used to treat / prevent the condition being targeted.

Controlled Trial – A type of clinical trial that includes a control group.

Double Blinded Trial – A blinded study where both the investigators and participants are not aware of which groups of participants received the intervention being studied.

Eligibility Criteria – The key criteria that applicants must meet in order to be enrolled or allowed to participate in a clinical study.

Enrollment – The act of registering a participant in a clinical trial or the number of participants in a trial.

Exclusion Criteria – The characteristics of a potential participant that would prevent them from being enrolled in a particular clinical study.

Experimental Arm – The group of participants receiving the intervention being studied.

Inclusion Criteria – The characteristics that a potential participant must meet in order to participate in a particular clinical study.

Informed Consent – The goal of the process of informed consent is to protect those volunteers taking part in a clinical study. The investigators must fulfill the following:

(1) They must provide all relevant and important details of the study including potential risks so that the potential participant may make a decision about whether or not to be enrolled.

(2) They must ensure that the information is conveyed appropriately so that the potential subjects understand what is being communicated to them.

(3) Ensure that potential participants recognize that their involvement is completely voluntary and that they may withdraw at any point during the study.

Intervention – That which is being studied and thought to have a positive impact on human health. This may include a drug, procedure, device or any other product or therapy.

Observational Study – A study where the participants are followed but there are no interventions implemented.

Open Label – The opposite of a blinded study. A trial where both the participants and investigators know who received the intervention.

Outcome Measure – The result that investigators are anticipating will occur with the particular intervention being studied. In other words, the effect of the intervention that the investigators are expecting.

Phase – Describes the sequential steps that must be taken in the investigation of an intervention prior to its approval for use. There are many phases a new drug or intervention must go through to demonstrate safety and efficacy in humans.

Placebo – A medication that is designed to be identical to the drug being studied but does not contain the active medicinal ingredient. This is used to rule out any psychological effect of the intervention and is often used in the control group.

Primary Outcome Measure – The most important outcome measure that the intervention is thought to change – the purpose of the study.

Principal Investigator – The person responsible for the entire scientific study.

Protocol -The document that describes the entire description of a study including its objectives, design and methodology.

Randomization– A process whereby participants are assigned to any group in a study by chance, not by specific criteria.

Recruiting – A study is said to be recruiting when it is open to enroll participants.

Secondary Outcome – A planned outcome measure that is less important than the primary outcome measure but is still of interest to investigators to see if the intervention being studied, had any effect.

Sham Comparator Arm – A group of participants that undergo a procedure or therapy (not a drug) or use a device that has no active effect. The data collected is used to compare to the treatment group that received the actual active procedure or device.

Single Blinded Study – A blinded study where either the investigators or the participants do not know which groups received the intervention being studied.

Study Design – The actual detailed protocol that a clinical study will follow including recruitment, sequence of events, allocation of participants into various arms, blinding methods, collection of data and so forth.

For a more complete list please see the website, a service of the U.S. National Institutes of Health.

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