Prevention Book


Fagan Nomogram

Aka: Fagan Nomogram
  1. See Also
    1. Screening Test
    2. Contingency Grid or Cross Tab (includes Statistics Example)
    3. Bayes Theorem (Bayesian Statistics)
    4. Experimental Error (Experimental Bias)
    5. Lead-Time Bias
    6. Length Bias
    7. Selection Bias (Screening 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. Background
    1. Paper based nomogram in slide-rule fashion calculates Post-Test Probability given Pre-Test Probability (Prevalence) and Likelihood Ratio
  3. Technique
    1. Start with a blank Fagan Nomogram
    2. Mark the Pre-Test Probability (diseases Prevalence) on the axis in the left hand column
    3. Mark the Likelihood Ratio (positive or negative) for the given test on the axis in the middle column
    4. Draw a line from the Pre-Test Probability point, through the Likelihood Ratio and intersect the third column axis (Post-Test Probability)
    5. Read the Post-Test Probability where the line intersects the axis on the third column
      1. If Positive Likelihood Ratio (LR+) is used, the Post-Test Probability will reflect how likely it is for a positive test to be a true positive for disease
      2. If Negative Likelihood Ratio (LR-) is used, the Post-Test Probability will reflect how likely it is for a negative test to be a true negative for disease
  4. Resources
    1. Diagnostic Test Calculator

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