NCI Dictionary of Cancer Terms

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The NCI Dictionary of Cancer Terms features 7,798 terms related to cancer and medicine.

Browse the dictionary by selecting a letter of the alphabet or by entering a cancer-related word or phrase in the search box.

selection bias
(seh-LEK-shun BY-us)
An error in choosing the individuals or groups to take part in a study. Ideally, the subjects in a study should be very similar to one another and to the larger population from which they are drawn (for example, all individuals with the same disease or condition). If there are important differences, the results of the study may not be valid.