Lead time bias
Lead time bias happens when
Relationship between screening and survival
The goal of screening is earlier detection (to diagnose a disease earlier than it would be without screening). Therefore, if screening works, it needs to advance in time to the moment of diagnosis. In other words, screening needs to introduce a lead time. However, the lead time itself biases survival statistics: people with diseases detected by screening appear to have a longer survival (the time the person has lived after diagnosis) only because screening starts the clock sooner.[citation needed]
Consider, for instance, a disease where there is no screening that is diagnosed by symptoms when patients are 60 years old and kills them when they are 65 years old. These patients lived 5 years after the diagnosis. Now, consider that with screening, the disease is detected when the patients are 55 years old, but they still die when they are 65. They did not live any longer because of earlier detection, but they survived 10 years after the diagnosis (only because the disease was diagnosed 5 years earlier). Therefore, earlier detection alone is not enough to achieve longer survival.[citation needed]
Lead time bias affects the interpretation of the five-year survival rate, effectively making it appear that people survive longer with cancer even in cases where the course of cancer is the same as in those who were diagnosed later.[3]
Another example is when early diagnosis by screening may not prolong the life of someone but just determine the propensity of the person to a disease or medical condition, such as by
See also
Notes
- ^ ISBN 978-0-8151-4385-7, retrieved 2021-01-14
- ^ "GPnotebook". gpnotebook.com.
- ISBN 978-1-4160-4002-6.