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How Are Clinical Studies of Mental Disorders Designed?

Clinical researchers call the standard scientific approach for trying out treatments a double-blind, randomized, controlled clinical trial. Understanding this term, and knowing how and why this approach is used, should help you to decide whether to become a research volunteer.

An important part of scientific research is comparison. Clinical research often will compare an investigational treatment to one that is used frequently and thus has familiar, or predictable, effects. To make the comparison useful, the investigator must try both methods on similar groups of subjects.

Researchers call the treatment with the predictable or known effect the control. The control may be a standard, commonly used treatment, or it may be a placebo. A placebo is something that does not directly affect the illness or symptoms under study in any specific way. (You may have heard a placebo described as a “sugar pill.”) Some studies use both a standard treatment and a placebo as controls.

The control helps an investigator find out if any changes seen in patients in the experimental group are, in fact, due to the new treatment.

The term randomized means how a researcher assigns each patient to a particular treatment under study. Researchers assign patients by chance either to a group taking the new treatment (called the treatment group) or to a group taking a standard treatment or a placebo (called the control group). This method, called randomization, helps avoid bias: having the study’s results affected by human choices or other factors not related to the treatments being tested. In some studies, researchers do not tell the patient whether he or she is in the treatment or control group (called a single-blind study). This approach is another way to avoid bias, because when people know what drug they are taking, it might change the way they react. For instance, patients who knew they were taking the new treatment might expect it to work better and report hopeful signs because they want to believe they are getting well. This could bias the study by making the results look better than they really were.

Random assignment helps to make sure that those in the group who receive an investigational treatment are similar to those in the group who receive the control treatment. By making certain that all who take part are similar, random assignment helps a researcher to make better conclusions.

The term double-blind in research design means that neither you nor the researcher will know if you are assigned to the experimental or to the control group. The aim is to avoid letting either the investigator’s hopes or expectations about a particular treatment or your hopes and expectations influence the manner in which he or she views improvements and side effects.

Your random assignment to a particular treatment group usually will occur after the researcher decides that you can be in the study, and after you agree to join the research by signing an informed consent form. Informed consent, which is key to the successful conduct of all clinical research, is discussed later in this pamphlet.

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How Are Clinical Studies of Mental Disorders Designed?

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APA Reference
Psych Central. (2020). How Are Clinical Studies of Mental Disorders Designed?. Psych Central. Retrieved on November 29, 2020, from
Scientifically Reviewed
Last updated: 14 Jan 2020 (Originally: 17 May 2016)
Last reviewed: By a member of our scientific advisory board on 14 Jan 2020
Published on Psych All rights reserved.