Here’s What We Know: The ABCs of Clinical Trial Terminology

If you are considering joining a clinical trial, you will hear many new words and phrases. It’s important to understand these terms before you decide to participate. Clinical trials, also called clinical research or research studies, test whether a new medical plan, device or treatment is safe and effective for people. These studies help advance medicine and protect public health 

To help you navigate the process, here is a simple glossary of common terms you should know.  

Adverse event  

Sometimes called a side effect, an adverse event is any unwanted or harmful experience a participant has during a clinical trial. It may or may not be caused by the treatment being studied and can range from mild to severe.  

Baseline characteristics 

This data includes details collected about each participant at the start of a study. It can include demographics, such as age, race and gender, and any measures specific to the study. For example, a clinical study related to depression may ask if participants have used antidepressants before. 

Blinding  

Also called masking, this is a procedure where some people are unaware of which treatment the participants receive. The goal is to prevent bias in the study results. 

  • Single-blind (single-masked) study: Participants do not know which treatment group they are in, but the research team does. 
  • Double-blind (double-masked) study: Neither the participants nor the research team knows who has been assigned to each treatment group. Usually, only the pharmacist knows which treatment is being administered to whom. 

Confidentiality  

This is the practice of keeping participants’ personal and medical information private. Researchers share study results as overall trends without naming participants or sharing private details unless they get permission. 

Control group  

This group of participants receives a comparison intervention, which could be the standard treatment, no intervention or a placebo. Researchers compare the control group’s results with the experimental group’s results to see how well the new treatment works.  

Eligibility criteria  

These are the rules about who can or cannot participate in a clinical study.  

  • Inclusion criteria: Factors that allow someone to participate  
  • Exclusion criteria: Factors that prevent someone from participating  

Experimental group  

This group of participants receives the new treatment or intervention being tested in the study. 

Human subjects protection review board 

Also called an institutional review board (IRB) or an ethics committee, a protection review board is a group of people who review, approve and monitor the clinical study’s protocol. Their role is to protect the rights and wellbeing of study participants. 

Informed consent  

This important process gives potential participants the key facts about a study, including its purpose, duration, procedures and potential risks and benefits, before they decide to participate. If a person agrees to enroll, they sign an informed consent form saying they understand and accept the study rules. This is not a contract, and a participant can leave the study at any time. 

Intervention  

This is the treatment, experimental drug or procedure that researchers test in the trial. Participants receive specific interventions to see their effects on health. This differs from an observational study, where investigators assess health outcomes in participants without assigning specific treatments.  

Outcome measure  

This is a planned measurement to determine how well the intervention works. Researchers use it to evaluate the intervention's effects on participants.  

Participants (subjects)  

These are the people in a clinical trial. 

  • Healthy volunteer: Someone with no known health problems who volunteers to test a new drug or intervention 
  • Patient volunteer: Someone with a known health problem who joins a study to better understand, diagnose or treat their condition 

Phases of clinical trials  

Clinical trials happen in phases, each answering different questions.  

  • Phase I: Tests safety and dosage in a small group of people (20-80 subjects)  
  • Phase II: Examines effectiveness and safety in a larger group (100-300 subjects)  
  • Phase III: Confirms effectiveness and monitors side effects in large groups (hundreds to thousands of subjects). These trials can lead to FDA approval. 
  • Phase IV: Happens after FDA approval to gather additional information on the drug’s risks, benefits and best use. 

Placebo  

A placebo is an inactive substance, such as a pill or liquid, that looks like the new treatment but has no active ingredients. Some studies use placebos to compare how well the experimental treatment works.  

Principal investigator  

This doctor or medical professional leads the research team at a study site. They guide the trial and make sure it runs safely and properly. 

Randomization  

This is the process of assigning participants to treatment groups by chance rather than by choice. Randomization helps reduce bias by giving every participant an equal chance of being assigned to any group in the trial. 

Sponsor  

This is the organization or person who oversees the clinical study and data analysis. Often, the sponsor will also fund the trial. 

Subject  

A subject is a participant in a study. 

Treatment arm  

This is a group of participants receiving a specific intervention in the trial. Some trials may have multiple treatment arms to compare different medications or dosages against a placebo or standard of care. 

Conclusion  

Weill Cornell Medicine is a leading center for clinical research, dedicated to cutting-edge medical discoveries and innovative treatments. Our expert teams work closely with patients to advance science and improve health outcomes. Through rigorous studies and compassionate care, Weill Cornell Medicine drives progress that shapes the future of medicine.  

If you are interested in participating in a clinical trial that can offer access to new treatments and help advance medical knowledge, connect with the Joint Clinical Trials Office at Weill Cornell Medicine and NewYork-Presbyterian. 

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