Clinical Trials Research Alliance (CTRA)

Glossary of Terms

Clinical Research Coordinator

A clinical research coordinator works with the trial’s principal investigator to make sure the trial is done according to the protocol and that participants’ health is being monitored regularly.

Clinical trial

A clinical trial is medical research that involves people to test new treatments and therapies.

Control Population

Study participants who do not receive the treatment being studied. This group’s outcome is compared to the group who did receive the treatment to see how the treatment worked.

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 treatment.

Inclusion/Exclusion Criteria

Inclusion criteria are factors that allow someone to participate in a clinical trial, such as the correct gender or age. Exclusion criteria are factors that exclude or do not allow participation.

Informed Consent

Informed consent explains the risks and potential benefits of a clinical trial before a volunteer decides whether to participate or not.

Patient Volunteer

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

Peer-Reviewed Scientific Journals

Peer review is a process by which experts review the report before it is published to ensure that the analysis and conclusions are sound.

Phases of Clinical Trials

Clinical trials are conducted in “phases.” The trials at each phase have a different purpose and help researchers answer different questions.

  • Phase I trials—An experimental drug or treatment is tested in a small group of people (20–80) for the first time. The purpose is to evaluate its safety and identify side effects.
  • Phase II trials—The experimental drug or treatment is administered to a larger group of people (100–300) to determine its effectiveness and to further evaluate its safety.
  • Phase III trials—The experimental drug or treatment is administered to large groups of people (1,000–3,000) to confirm its effectiveness, monitor side effects, and to compare it with standard or equivalent treatments.
  • Phase IV trials—After a drug is licensed and approved by the FDA, researchers track its safety, seeking more information about its risks, benefits, and optimal use.


A placebo is a pill or liquid that looks like the treatment being studied but does not have any treatment value from active ingredients.

Principal Investigator

A Principal Investigator is a doctor who leads the clinical research team and, along with the other members of the research team, regularly monitors study participants’ health to determine the study’s safety and effectiveness.


A Protocol is a carefully designed plan to protect the participants’ health and answer specific research questions.


Randomization is the process by which two or more alternative treatments are assigned to volunteers by chance rather than by choice.

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 if they are receiving the investigational treatment or a placebo, so the participants can describe what happens without bias.

Types of Clinical Trials

  • Diagnostic trials determine better tests or procedures for diagnosing a particular disease or condition.
  • Natural history studies provide valuable information about how disease and health progress.
  • Prevention trials look for better ways to prevent a disease in people who have never had the disease or to prevent the disease from returning.
  • Quality of life trials (or supportive care trials) explore and measure ways to improve the comfort and quality of life of people with a chronic illness.
  • Screening trials test the best way to detect certain diseases or health conditions.
  • Treatment trials test new treatments, new combinations of drugs, or new approaches to surgery or radiation therapy.
Last edited on 09/27/2018.