II. Definition
- Early diagnosis falsely appears to prolong survival
III. Example
- Disease 'A' is 100% fatal
- Disease 'A' lasts 7 years from onset to death
- Disease 'A' patients are asymptomatic for 4 years
- Disease 'A' median survival 3 years after diagnosis
-
Screening Test can identify Disease 'A' early
- Detection occurs 2 years before clinical diagnosis
- Disease 'A' still lasts 7 years before death
- Disease 'A' is now asymptomatic for 2 years
- Disease 'A' median survival 5 years after diagnosis
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Screening Test falsely appears to prolong survival
- Screened and unscreened patients each survive 7 years
- Screened patients know diagnosis 2 years earlier