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).

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.^[1]

Lead time bias occurs when testing increases perceived survival time without affecting the course of the disease.

Relationship between screening and survival

Main article: Screening (medicine)

By screening, the intention is to diagnose a disease earlier than it would be without screening. Without screening, the disease may be discovered later when symptoms appear.

Early diagnosis through screening may not prolong the life of someone, just determine the propensity of the person to a disease or medical condition such as through DNA testing. No additional life span has been gained; the patient may be subject to added anxiety as the patient must live for longer with knowledge of the disease. For example, the genetic disorder Huntington's disease is diagnosed when symptoms appear around age 50, and the person dies around age 65. The typical patient therefore lives about 15 years after diagnosis. A genetic test at birth makes it possible to diagnose this disorder earlier. If this newborn baby dies around age 65, he or she will have "survived" 65 years after diagnosis, without having actually lived any longer than those diagnosed without DNA detection.

Raw statistics can make screening appear to increase survival time (this gain is called lead time). If the person dies at a time in life that previously has been the usual course of the disease, than when detected by early screening, then the person's life has not been prolonged. Detection through advanced screening does not always mean prolong survival.

Lead time bias can affect interpretation of the five-year survival rate.^[2]

Notes

↑ Lead time bias - General Practice Notebook
↑ Gordis, Leon (2008). Epidemiology: with STUDENT CONSULT Online Access. Philadelphia: Saunders. p. 318. ISBN 1-4160-4002-1.

Biases

Biases in judgment and decision-making	Acquiescence bias Anchoring bias Attentional bias Attribution bias Belief bias Choice-supportive bias Cognitive bias Confirmation bias Congruence bias Correspondence bias Halo effect Hindsight bias Hostile attribution bias Memory bias Outcome bias Response bias Self-serving bias Status quo bias Survivorship bias

Statistical biases	Bias of an estimator Information bias Lead time bias Omitted-variable bias Sampling bias Selection bias Self-selection bias Social desirability bias Spectrum bias Systematic error Systemic bias

Other	Academic bias FUTON bias Media bias No abstract available bias Publication bias Reporting bias

Lead time bias

Relationship between screening and survival

Notes

See also