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Glossary of Terms

We know that many of the concepts used on this site can be difficult to understand. For that reason, we have provided you with a glossary to help you make sense of the terms used in Comparative Effectiveness Research. Every word that is defined in this glossary should appear highlighted throughout the Web site. When you come upon a highlighted term and would like to read the full definition, you can either click on the word to visit the glossary or roll your mouse over the word for a pop-up definition.



Clinical Research

The branch of medical science devoted to finding information that improves people's health. It includes research studies that examine the safety and effectiveness of medications, medical devices, diagnostic tests, and treatment regimens intended for human use. Usually, more than one person with the same disease is studied. detail

Clinical Trial

A carefully conducted research study that compares the effects of drugs, treatments, or diagnostic tests. detail


A group of people with some characteristic in common. The characteristic can be:

  • Where people live.
  • Where they work.
  • Where they go to school.
  • People of the same age.
  • People with the same medical condition.
  • People receiving the same medical treatment.

Cohort Study

A clinical research study in which people who presently have a certain condition or receive a particular treatment are followed over time and compared with another group of people who are not affected by the condition. detail

Comparative Effectiveness

A type of health care research that compares the results of one approach for managing a disease to the results of other approaches. Comparative effectiveness usually compares two or more types of treatment, such as different drugs, for the same disease. Comparative effectiveness also can compare types of surgery or other kinds of medical procedures and tests. The results often are summarized in a systematic review. detail

Confidence Interval

The range in which a particular result (such as a laboratory test) is likely to occur for everyone who has a disease. "Likely" usually means 95 percent of the time.

Clinical research studies are conducted on only a certain number of people with a disease rather than all the people who have the disease. The study's results are true for the people who were in the study but not necessarily for everyone who has the disease.

The confidence interval is a statistical estimate of how much the study findings would vary if other different people participated in the study. A confidence interval is defined by two numbers, one lower than the result found in the study and the other higher than the study's result. The size of the confidence interval is the difference between these two numbers. detail

Control Group

In a research study, the group of people who do not receive the treatment being tested. The control group might receive a placebo, a different treatment for the disease, or no treatment at all. detail

Controlled Clinical Trial

A type of clinical trial comparing the effectiveness of one medication or treatment with the effectiveness of another medication or treatment. In many controlled trials, the other treatment is a placebo (inactive substance) and is considered the "control." detail

Cost-Benefit Analysis

A type of analysis that compares the financial costs with the benefits of two or more health care treatments or programs. Health care interventions that have the same or better benefit at a lower cost are better values than treatments or programs that are more expensive. detail

Cost-Effectiveness Analysis

A type of analysis that is similar to a cost-benefit analysis but is used when the benefits cannot be measured in financial terms or dollars. It would be hard to put a price-tag on living an extra year of life. detail