Glossary of Common Site Terms


Accepts healthy volunteers

A type of eligibility criteria that indicates whether people who do not have the condition/disease being studied can participate in that clinical study.

Active comparator arm

An arm type in which a group of participants receives an intervention/treatment considered to be effective (or active) by health care providers.

Adverse event

An unfavorable change in the health of a participant, including abnormal laboratory findings, that happens during a clinical study or within a certain amount of time after the study has ended. This change may or may not be caused by the intervention/treatment being studied.

Age or age group

A type of eligibility criteria that indicates the age a person must be to participate in a clinical study. This may be indicated by a specific age or the following age groups:

The age groups are:

  • Child (birth-17)

  • Adult (18-65)

  • Senior (66+)


A method used to assign participants to an arm of a clinical study. The types of allocation are randomized allocation and nonrandomized.


A group or subgroup of participants in a clinical trial that receives a specific intervention/treatment, or no intervention, according to the trial's protocol.

Arm type

A general description of the clinical trial arm. It identifies the role of the intervention that participants receive. Types of arms include experimental arm, active comparator arm, placebo comparator arm, sham comparator arm, and no intervention arm.

Baseline characteristics

Data collected at the beginning of a clinical study for all participants and for each arm or comparison group. These data include demographics, such as age, sex/gender, race and ethnicity, and study-specific measures (for example, systolic blood pressure, prior antidepressant treatment).

Certain agreements

Information required by the Food and Drug Administration Amendments Act of 2007. In general, this is a description of any agreement between the sponsor of a clinical study and the principal investigator (PI) that does not allow the PI to discuss the results of the study or publish the study results in a scientific or academic journal after the study is completed.

City and distance

In the search feature, the City field is used to find clinical studies with locations in a specific city. The Distance field is used to find studies with locations within the specified distance from a city in number of miles. For example, if you choose Illinois as the state, identifying "Chicago" as the city and "100 miles" as the distance will find all studies listing a location within 100 miles of Chicago.

Clinical study

A research study involving human volunteers (also called par