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Clinical Trial Terminology Explained

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The National Cancer Institute estimates that between 5% and 8% of cancer patients participate in clinical trials. Why is the number so low? Part of the problem is that many patients believe that all clinical trials include a placebo (an inactive treatment with no known therapeutic value) and treat participants like "guinea pigs" -- neither of which is true. To help clear up the confusion, this Health Alert explains clinical trial terminology, including randomization, placebo, and blinding.

Clinical trials are studies conducted in humans to identify new methods of screening, preventing, diagnosing, or treating a disease or to compare innovative approaches to treatment with the standard treatments currently in use. Before researchers conduct a clinical trial, the treatment has usually gone through extensive laboratory and animal testing. Once researchers have good evidence from these preclinical studies that a treatment might work in people, they can request approval from the U.S. Food and Drug Administration to test it in humans.

When considering clinical trials, you'll be confronted with a host of terms that may be unfamiliar. For example:


  • Randomization. If you enter a randomized clinical trial, you will be assigned by chance to a control group or a treatment group. If you are assigned to the control group, you will receive the standard treatment or procedure -- the one you would receive if you were not participating in the study. If you are assigned to the treatment group, you will receive the experimental treatment or procedure.
  • Placebo group. In some phase II and III clinical trials, participants are assigned to a placebo group instead of a control group and receive an inactive pill or sham treatment that has no effect on the disease. Placebos are never used when a patient could benefit from a known effective treatment; thus, most cancer treatment trials do not have a placebo group. However, a placebo group may be used if there is no standard therapy with which to compare the experimental treatment. A placebo is also sometimes used in studies where everyone receives the standard treatment but half also receive an experimental treatment and half a placebo.
  • Blinding. Some randomized clinical trials are "blinded," meaning you won't know whether you are getting the treatment being studied or the standard treatment until the trial is over. In a "double-blinded" clinical trial, neither you nor the investigators will know which treatment you are getting until the trial has ended. This practice minimizes the chances that a treatment seems to work only because of the expectations or biases of those involved in the study. Blinding is often done when a placebo is included in one part of the clinical trial.


Posted in Prostate Disorders on December 17, 2009
Reviewed January 2011

Medical Disclaimer: This information is not intended to substitute for the advice of a physician. Click here for additional information: Johns Hopkins Health Alerts Disclaimer

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