Prevention Book


Length Bias

Aka: Length Bias, Length-Time Bias
  1. See Also
    1. Screening Test
    2. Contingency Grid or Cross Tab (includes Statistics Example)
    3. Bayes Theorem (Bayesian Statistics)
    4. Fagan Nomogram
    5. Experimental Error (Experimental Bias)
    6. Lead-Time Bias
    7. Selection Bias
    8. Likelihood Ratio (Positive Likelihood Ratio, Negative Likelihood Ratio)
    9. Number Needed to Screen (Number Needed to Treat, Absolute Risk Reduction, Relative Risk Reduction)
    10. Negative Predictive Value
    11. Positive Predictive Value
    12. Pre-Test Odds or Post-Test Odds
    13. Receiver Operating Characteristic
    14. Test Sensitivity (False Negative Rate)
    15. Test Specificity (False Positive Rate)
    16. U.S. Preventive Services Task Force Recommendations
  2. Definition
    1. Screening over-represents less aggressive disease
  3. Example
    1. Aggressive disease has a short asymptomatic period
      1. Screening is unlikely to detect these patients early
      2. Clinical diagnosis will identify by symptoms
      3. Over-represented in clinical diagnosis cohort
    2. Less aggressive disease has longer asymptomatic period
      1. Disease often detected by screening
      2. Over-represented in screening cohort
    3. Screening program falsely appears to improve survival
      1. Less aggressive disease common in screening group
      2. Screening cohort has a better prognosis by definition
  4. References
    1. Gates (2001) Am Fam Physician 63(3):513-22 [PubMed]
    2. MacLean (1996) Med Clin North Am 80(1):1-14 [PubMed]
    3. Nielsen (1999) Med Clin North Am 83(6):1323-37 [PubMed]

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