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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.

 

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Placebo Effect

Definition: A physical or emotional change that occurs after a participant in a research study takes a placebo. The change, which may include the lessening of symptoms, is not the result of chemical effects of the placebo because the placebo does not contain any active ingredients. The change is often based on the participant's or researcher's expectation that a change will occur.

Example: In a large research study of people with arthritis of the knee, one group of participants took a placebo pill. Sixty percent of these people reported improvement in their pain and functioning while taking the pill. This clinical improvement was considered to be a placebo effect.

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