II. Definition

  1. Early diagnosis falsely appears to prolong survival

III. Example

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

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