**Fagan Nomogram**

- See Also

- Screening Test
- Contingency Grid or Cross Tab (includes Statistics Example)
- Bayes Theorem (Bayesian Statistics)
- Experimental Error (Experimental Bias)
- Lead-Time Bias
- Length Bias
- Selection Bias (Screening Bias)
- Likelihood Ratio (Positive Likelihood Ratio, Negative Likelihood Ratio)
- Number Needed to Screen (Number Needed to Treat, Absolute Risk Reduction, Relative Risk Reduction)
- Negative Predictive Value
- Positive Predictive Value
- Pre-Test Odds or Post-Test Odds
- Receiver Operating Characteristic
- Test Sensitivity (False Negative Rate)
- Test Specificity (False Positive Rate)
- U.S. Preventive Services Task Force Recommendations

- Background

- Paper based nomogram in slide-rule fashion calculates Post-Test Probability given Pre-Test Probability (Prevalence) and Likelihood Ratio

- Technique

- Start with a blank Fagan Nomogram
- Mark the Pre-Test Probability (diseases Prevalence) on the axis in the left hand column
- Mark the Likelihood Ratio (positive or negative) for the given test on the axis in the middle column
- Draw a line from the Pre-Test Probability point, through the Likelihood Ratio and intersect the third column axis (Post-Test Probability)
- Read the Post-Test Probability where the line intersects the axis on the third column
- 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
- 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

- Resources

- Diagnostic Test Calculator