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Lead-Time Bias

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  1. Definition
    1. Early diagnosis falsely appears to prolong survival
  2. 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
  3. References
    1. Gates (2001) Am Fam Physician 63(3):513
    2. MacLean (1996) Med Clin North Am 80(1):1
    3. Nielsen (1999) Med Clin North Am 83(6):1323

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