Evaluation Glossary

Selection Bias

Potential biases introduced into a study by the selection of different types of people into treatment and comparison groups. As a result, the outcome differences may potentially be explained as a result of pre-existing differences between the groups, as opposed to the treatment itself.


US Environmental Protection Agency. (2007). Program Evaluation Glossary. Office of the Administrator/Office of Policy/Office of Strategic Environmental Management/Evaluation Support Division.

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