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Selection bias

A systematic distortion caused by how cases enter, remain in, or leave a sample.

Published 04 August 2026Updated 04 August 2026

Selection bias makes a sample differ from the population it is meant to represent because inclusion is related to the outcome or exposure being studied. Examine recruitment, eligibility, attrition, and who had no chance to appear in the data.

Sources

Cochrane Risk of Bias Tools

Cochrane / 2023 / Website

Bias assessment reference for evidence review.