Systematic difference in how outcomes are measured or verified between comparison groups.
Detection bias (also called ascertainment bias) occurs when outcome assessment is influenced by knowledge of which group a participant is in, leading to differential measurement, diagnosis, or classification of outcomes across arms. It is most effectively controlled by blinding outcome assessors and using standardised, objective measurement criteria; risk is highest when outcomes are subjective (e.g., pain ratings, clinician-judged healing) rather than hard endpoints (e.g., mortality, imaging-confirmed fracture). Some frameworks group detection bias under the broader umbrella of measurement or observer bias, so terminology varies between appraisal tools.
This guide was auto-drafted and is pending editorial review.