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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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Selection Bias

Definition: A type of bias caused by an error in the way people are assigned to groups in a clinical research study. This can occur when the study and control groups are chosen so that they differ from each other in ways that may affect the outcome of the study.

Example: For example, a research study compared rates of side effects in men who received surgical removal of the prostate with rates in men who received radiation therapy for prostate cancer. The men in the two groups differed in their age and the rates of other medical problems. Because of this selection bias, differences in the side effect rates may not be due just to the effects of the type of treatment.

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