Lead time bias

Lead time is the length of time between the detection of a disease (usually based on new, experimental criteria) and its usual clinical presentation and diagnosis (based on traditional criteria). OR It is the time between early diagnosis with screening, and when diagnosis would have been made without screening. Lead time bias is that factor when comparing, in detection of disease, a traditional test with a new or experimental test but the outcome of the disease is unchanged; the new or experimental test merely identifies the disease earlier than the previous and thus gives the impression that survival is prolonged. It is an important factor when evaluating the effectiveness of a specific test.