Adverse Reaction

An unwanted effect caused by the administration of the treatment. Occurrence may be immediate or develop over time.

Related Terms: Adverse Event


A study “arm” is any of the treatment groups in a randomized trial. Most randomized trials have two “arms,” but some have three “arms,” or even more.

Related Terms: Randomized Trial


The initial time point in a clinical trial, just before a participant starts to receive the experimental treatment which is being tested. At this reference point, measurable values such as the level and composition of depressive symptoms are recorded. The safety and efficacy of a new treatment are often determined by monitoring changes from “baseline” values.


When a point of view prevents impartial judgment on issues relating to the subject of that point of view. In clinical studies, bias is usually controlled through blinding and randomization.

Related Terms: Blind, Randomization


A clinical trial is “blind” if participants are unaware of whether they are in the experimental or control arm (group) of the study; also called masked.

Blinded Study

A clinical trial design in which neither the participants nor the research staff knows which participants are receiving the experimental treatment and which are receiving a placebo (inactive treatment). Blinded trials are thought to produce the most unbiased results, since the expectations of the research staff and the participant about the treatment being evaluated do not affect the outcome.

Related Terms: Blind, Placebo, Controlled Study

Cleared Device

In the U. S., the Food and Drug Administration (FDA) must clear a device before it can be marketed (offered for sale to physicians for a specific clinical use). The clearance process involves several steps that may include pre-clinical laboratory and animal studies, clinical trials for safety and efficacy, filing of an application by the manufacturer of the device, FDA review of the application, and FDA clearance/rejection of the application.

Related Terms: Food and Drug Administration

Clinical Investigator

A professional medical researcher involved in the carrying out a clinical trial protocol.

Clinical Trial

A clinical trial is a research study that answers specific questions about a treatment. Clinical trials (often called medical research, research studies, or treatment trials) are usually used to determine if a treatment is safe and effective for the disorder under study. Well conducted clinical trials are the fastest and safest way to develop new treatments.


A specific circumstance under which a treatment should not be used. In this circumstance, the treatment could be harmful or result in serious injury or death.

Control Group

The standard against which an experimental treatment is evaluated. In a controlled clinical trial, one or more groups of patients will be given an experimental treatment, while the control group is given either a standard treatment for the disorder or a placebo.

Related Terms: Placebo, Standard Treatment

Controlled Trials

Clinical trials that incorporate a control group. In clinical trials, one group of participants are given an experimental treatment while another group is given either a standard treatment for the disorder, or a sham inactive treatment.

Related Terms: Control Group, Inactive Treatment

Data Safety Monitoring Board (DSMB)

An independent committee of clinical research experts that reviews data while a clinical trial is in progress to ensure that participants are not exposed to undue risk. A DSMB may recommend that a trial be stopped if there are safety concerns or if the trial objectives have been achieved prior to completing all planned patient enrollment. A DSMB may look at unblinded data where the study is still underway.

Abbreviations: DSMB


Evidence that the treatment provides benefit for the disorder under study. In a procedure mandated by the FDA, all new device treatments must establish efficacy requirements before they are approved or cleared for use in the US.

Related Terms: Food and Drug Administration

Eligibility Criteria

A set of criteria for participant selection; includes Inclusion and Exclusion criteria.

Related Terms: Inclusion/Exclusion Criteria

Food and Drug Administration (FDA)

The U.S. Department of Health and Human Services agency responsible for evaluating the safety and effectiveness of all drugs, vaccines, and medical devices. Internet address:

Abbreviations: FDA

Inclusion/Exclusion Criteria

The factors determining whether a person may or may not be allowed to enter a clinical trial. These criteria are based on such factors as age, gender, the type and stage of a disease, previous treatment history, and other medical conditions. It is important to note that inclusion and exclusion criteria are not used to reject people personally, but rather to identify appropriate participants and keep them safe.

Institutional Review Board (IRB)

A committee of physicians, statisticians, researchers, patient advocates, and other community members not involved in the clinical trial whose responsibility it is to ensure a clinical trial is ethical and that the rights of study participants are protected. In the US and many other countries, all clinical trials must be approved by an IRB before they are allowed to begin. Every organization that conducts medical research involving human participants must, by federal regulation, have IRB approval (and periodic reviews) of the research in order to protect the rights of human participants.

Abbreviations: IRB

Intent to Treat

A type of analysis use for evaluating clinical trial results that includes all data from participants in the groups to which they were randomized even if they never received the experimental treatment.

Related Terms: Randomization

Open-Label Trial

A clinical trial in which the research staff and participants know which treatment (active or inactive) is being administered to the participant.


A placebo (sometimes called a sham treatment), is a treatment that has no therapeutic value. In clinical trials, experimental treatments are often compared with a placebo to assess the treatment’s safety and effectiveness. In some studies, the participants in the control group will receive a placebo instead of the active treatment.

Related Terms: Sham Controlled Study

Placebo Effect

A physical or emotional change, occurring after a treatment is administered that is not the result of the treatment. The change may be beneficial, reflecting the expectations of the participant rather than the effect of the treatment itself.


A study plan on which all clinical trials are based. The plan is carefully designed to safeguard the health of the participants as well as answer specific scientific questions. A protocol describes what types of people may participate in the trial, schedule of events, evaluations, treatment procedures, medications dosages and/or device interventions, and the length of the study. Participants following a clinical trial protocol are seen regularly by research staff to receive the treatments, monitor their health and to determine the safety and effectiveness of their treatment.

Related Terms: Inclusion/Exclusion Criteria


A method by which study participants are assigned to a treatment group by chance (i.e. the flip of a coin). Randomization is intended to eliminate biased assignment to the different treatment groups in a clinical study. (See Arm.)

Randomized Trial

A study in which participants are randomly assigned to one of two or more treatment arms. Occasionally placebos are utilized in one of the arms.

Related Terms: Arm, Placebo

Sham Controlled Study

Related Terms: Controlled Study

Side Effects

Any undesired actions or effects of the treatment. These are tracked very carefully in a clinical trial.

Related Terms: Adverse Reaction

Standard Treatment

A standard treatment is a treatment for a given disorder that is typically widely used and well understood in terms of its safety and effectiveness.

Study Endpoint

A pre-defined measure used to determine the outcome of a study. This outcome may be a measure of effectiveness and/or safety as defined by the study design.