Screening Test

1. See Also
   1. Contingency Grid (includes Statistics Example)
   2. Test Sensitivity
   3. Test Specificity
   4. Negative Predictive Value
   5. Positive Predictive Value
   6. Likelihood Ratio
   7. Number Needed to Screen
   8. Length Bias
   9. Leadtime Bias
   10. Selection Bias
2. Definitions
   1. Factors affecting Positive Predictive Value
      1. Prevalence of disease
      2. Accuracy of test
3. Types: Bias
   1. Screening Bias
   2. Lead-Time Bias
   3. Length-Time Bias
4. Criteria: Ideal Screening Test
   1. Disease Features
      1. Disease significantly impacts public health
      2. Intermediate probability of disease
      3. Detection occurs before a critical point
         1. Critical point occurs before clinical diagnosis
            1. Screened patient is still asymptomatic
            2. Diagnosis would not otherwise occur this early
            3. Endometrial Cancer's critical point is too late
         2. Critical point occurs in time to affect outcome
            1. Disease must be detected early enough for cure
            2. Lung Cancer's critical point occurs too early
   2. Test Features
      1. High Test Sensitivity to detect asymptomatic disease
      2. High Test Specificity minimizes false positives
      3. Screening Test tolerated by patients
   3. Screened Population Features
      1. Disease has high enough Prevalence to allow screening
      2. Medical care available if Screening Test positive
      3. Patient willing to undergo further evaluation
5. References
   1. Gates (2001) Am Fam Physician 63(3):513-22
   2. MacLean (1996) Med Clin North Am 80(1):1-14
   3. Nielsen (1999) Med Clin North Am 83(6):1323-37