Glossary of Research Terms

This glossary has been created to help you better understand terms commonly used for research and clinical trials. Terms are listed alphabetically.



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.

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

Arm - 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.


Clinical Trial/Study - A systematic collection of data  involving human volunteers (also called participants) that is intended to add to medical knowledge. There are two types of clinical studies: interventional studies  and observational studies.

Cooperative Group - A group of researchers, cancer centers, and community doctors who are involved in studies that test new ways to screen, prevent, diagnose, and treat a certain disease group, such as, cancer. Clinical trials run by cooperative groups are funded and supported by federal agencies, for example, the National Cancer Institute (NCI), and large numbers of patients take part in many locations. The current U.S. cancer cooperative groups are the Alliance for Clinical Trials in Oncology, ECOG-ACRIN Cancer Research Group, SWOG, and Children’s Oncology Group (COG). The NCI clinical trials cooperative groups are part of the National Clinical Trials Network (NCTN).


Deviation (or protocol deviation) - Accidental or unintentional changes to, or non-compliance with the research protocol that does not increase risk or decrease benefit or; does not have a significant effect on the subject's rights, safety or welfare; and/or on the integrity of the data.

Diagnostic Trial - A type of clinical trial that determine better tests or procedures for diagnosing a particular disease or condition.


Eligibility Criteria - The key requirements that people who want to participate in a clinical study must meet or the characteristics they must have. Eligibility criteria consist of both inclusion criteria (which are required for a person to participate in the study) and exclusion criteria (which prevent a person from participating). Types of eligibility criteria include whether a study accepts healthy volunteers, has age or age group requirements, or is limited by sex.

Enrollment - The number of participants in a clinical study. The "estimated" enrollment is the target number of participants that the researchers need for the study.

Exclusion Criteria - A type of eligibility criteria. These are reasons that a person is not allowed to participate in a clinical study.

Expanded Access - A way for patients with serious diseases or conditions who cannot participate in a clinical trial to gain access to a medical product that has not been approved by the U.S. Food and Drug Administration (FDA). Also called compassionate use. There are different expanded access types.

Experimental Arm - An arm type in which a group of participants receives the intervention/treatment that is the focus of the clinical trial.


Group/Cohort - A group or subgroup of participants in an observational study that is assessed for biomedical or health outcomes.


Healthy Volunteer - A Healthy volunteer is a person with no known significant health problems who participates in clinical research to test a new drug, device, or intervention.

Human Subjects Protection Review Board - A group of people who review, approve, and monitor the clinical study's protocol. Their role is to protect the rights and welfare of people participating in a study (referred to as human research subjects), such as reviewing the informed consent form. The group typically includes people with varying backgrounds, including a community member, to make sure that research activities conducted by an organization are completely and adequately reviewed. Also called an institutional review board, or IRB, or an ethics committee.


Inclusion Criteria - A type of eligibility criteria. These are the reasons that a person is allowed to participate in a clinical study.

Informed Consent - A process used by researchers to communicate to potential and enrolled participants the risks and potential benefits of participating in a clinical study.

Informed Consent Form (ICF) - The document used in the informed consent or process.

Institutional Biosafety Committee - A group of experts and community members that is required to review research involving, but are not limited to, recombinant DNA, RNAi, pathogens, human materials, and other potentially infectious material as well as transgenic animals.

Intervention/Treatment - A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.

Intervention Study (Clinical Trial) - A type of clinical study in which participants are assigned to groups that receive one or more intervention/treatment (or no intervention) so that researchers can evaluate the effects of the interventions on biomedical or health-related outcomes. The assignments are determined by the study's protocol. Participants may receive diagnostic, therapeutic, or other types of interventions.

Investigator - A researcher involved in a clinical study. Related terms include site principal investigator, site sub-investigator, study chair, study director, and study principal investigator.


Masking - A clinical trial design strategy in which one or more parties involved in the trial, such as the investigator or participants, do not know which participants have been assigned which interventions. Types of masking include: open label, single blind masking, and double-blind masking.


Natural History Study - A type of study that provide valuable information about how disease and health progress.

NCT Number - A unique identification code given to each clinical study record registered on The format is "NCT" followed by an 8-digit number (for example, NCT00000419). Also called the identifier.

Non-intervention Arm - An arm type in which a group of participants does not receive any intervention/treatment during the clinical trial.


Observational Study - The general design of the strategy for identifying and following up with participants during an observational study. Types of observational study models include cohort, case-control, case-only, case-cross-over, ecologic or community studies, family-based, and other.

Other Adverse Event - An adverse event that is not a serious adverse event, meaning that it does not result in death, is not life-threatening, does not require inpatient hospitalization or extend a current hospital stay, does not result in an ongoing or significant incapacity or interfere substantially with normal life functions, and does not cause a congenital anomaly or birth defect; it also does not put the participant in danger and does not require medical or surgical intervention to prevent one of the results listed above.

Outcome Measure - For clinical trials, a planned measurement described in the protocol that is used to determine the effect of an intervention/treatment on participants. For observational studies, a measurement or observation that is used to describe patterns of diseases or traits, or associations with exposures, risk factors, or treatment. Types of outcome measures include primary outcome measure and secondary outcome measure.


Patient Volunteer - A patient volunteer has a known health problem and participates in research to better understand, diagnose, treat, or cure that disease or condition.

Phase - The stage of a clinical trial studying a drug or biological product, based on definitions developed by the U.S. Food and Drug Administration (FDA). The phase is based on the study's objective, the number of participants, and other characteristics. There are five phases: Early Phase 1 (formerly listed as Phase 0), Phase 1, Phase 2, Phase 3, and Phase 4. "N/A" (or not applicable) is used to describe trials without FDA-defined phases, including trials of devices or behavioral interventions.

Phase 1 - A phase of research to describe clinical trials that focus on the safety of a drug. They are usually conducted with healthy volunteers, and the goal is to determine the drug's most frequent and serious adverse events and, often, how the drug is broken down and excreted by the body. These trials usually involve a small number of participants.

Phase 2 - A phase of research to describe clinical trials that gather preliminary data on whether a drug works in people who have a certain condition/disease (that is, the drug's effectiveness). For example, participants receiving the drug may be compared to similar participants receiving a different treatment, usually an inactive substance (called a placebo) or a different drug. Safety continues to be evaluated, and short-term adverse events are studied.

Phase 3 - A phase of research to describe clinical trials that gather more information about a drug's safety and effectiveness by studying different populations and different dosages and by using the drug in combination with other drugs. These studies typically involve more participants.

Phase 4 - A phase of research to describe clinical trials occurring after FDA has approved a drug for marketing. They include postmarket requirement and commitment studies that are required of or agreed to by the study sponsor. These trials gather additional information about a drug's safety, efficacy, or optimal use.

Pivotal Trial - A clinical trial or study intended to provide evidence for a drug marketing approval, e.g. by the United States Food and Drug Administration. Phase III trials are assumed to be pivotal so the phrase is often used for the rare pivotal phase II trials.

Placebo - An inactive substance or treatment that looks the same as, and is given in the same way as, an active drug or intervention/treatment being studied.

Placebo Comparator Arm - An arm type in which a group of participants receives a placebo during a clinical trial.

Prevention Trial - A type of clinical trial that looks for better ways to prevent a disease in people who have never had the disease or to prevent the disease from returning.

Primary Purpose - The main reason for the clinical trial. The types of primary purpose are: treatment, prevention, diagnostic, supportive care, screening, health services research, basic science, and other.

Principal Investigator - The person who is responsible for the scientific and technical direction of the entire clinical study.

Protocol - The written description of a clinical study. It includes the study's objectives, design, and methods. It may also include relevant scientific background and statistical information.


Quality of Life Trial (or supportive care trials) - Clinical trials that explore and measure ways to improve the comfort and quality of life of people with a chronic illness.


Randomized Allocation - A type of allocation strategy in which participants are assigned to the arms of a clinical trial by chance.


Screening Trial - A type of clinical trial that tests the best way to detect certain diseases or health conditions.

Serious Adverse Event - An adverse event that results in death, is life-threatening, requires inpatient hospitalization or extends a current hospital stay, results in an ongoing or significant incapacity or interferes substantially with normal life functions, or causes a congenital anomaly or birth defect. Medical events that do not result in death, are not life-threatening, or do not require hospitalization may be considered serious adverse events if they put the participant in danger or require medical or surgical intervention to prevent one of the results listed above.

Single or Double-Blind Studies - Single- or double-blind studies (also called single- or double-masked studies) are studies in which the participants do not know which medicine is being used, so they can describe what happens without bias.

Sponsor - The organization or person who initiates the study and who has authority and control over the study.

Statistical Analysis Plan - The written description of the statistical considerations and methods for analyzing the data collected in the clinical study.

Study Design - The investigative methods and strategies used in the clinical study.


Treatment Trial - A clinical trial that is designed to test new treatments, new combinations of drugs, or new approaches to surgery or radiation therapy.


U.S. Food and Drug Administration (FDA) - An agency within the U.S. Department of Health and Human Services. The FDA is responsible for protecting the public health by making sure that human and veterinary drugs, vaccines and other biological products, medical devices, the Nation's food supply, cosmetics, dietary supplements, and products that give off radiation are safe, effective, and secure.

Common Acronyms

FDA: U.S. Food and Drug Administration

NIH: The National Institutes of Health

NSF: The National Science Foundation

NCI: National Cancer Institute

NRG Oncology: National Research Group for Oncology, a cooperative group

NSABP: National Surgical Adjuvant Breast and Bowel Project

ECOG-ACRIN: A cooperative group comprised of two combined groups, the Eastern Cooperative Oncology Group (ECOG) and the American College of Radiology Imagining Network (ACRIN)

Alliance: The Alliance for Clinical Trials in Oncology, a cooperative group.

SWOG: The SouthWest Oncology Group, a cooperative group

COG: Children's Oncology Group

IRB: Institutional Review Board, a type of Human Subjects Protection Review Board

IBC: Institutional Biosafety Committee, required for some types of research studies

SAE: Severe Adverse Event

AE: Other Adverse Event (non-severe)