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## Test Sensitivity

*Aka: Test Sensitivity, False Negative Rate*

- See Also
- Screening Test
- Contingency Grid or Cross Tab (includes Statistics Example)
- Bayes Theorem (Bayesian Statistics)
- Fagan Nomogram
- 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 Specificity (False Positive Rate)
- U.S. Preventive Services Task Force Recommendations

- Definition
- Screening Test's ability to identify true disease
- A Test with high sensitivity has few false negatives
- Independent of disease Prevalence in the community
- Sensitive Tests allow user to rule out a condition (mnemonic "SNout")

- Calculation
- Test Sensitivity
- True positive tests per total affected patients tested
- Test Sensitivity = P(positive test | disease)
- Where P (A | B) = Probability of A given B

- Expressed as a percentage

- False Negative Rate
- True cases missed by the Screening Test (test negative despite presence of condition)
- False Negative Rate = 1 - Test Sensitivity

- Test Sensitivity
- Example: A new Screening Test for Crohn's Disease
- Patients with known Crohn's Disease tested: 45
- Patients with known Crohn's Disease who have a positive test: 36
- Sensitivity = 36/45 or 80%

- References
- Hennekens (1987) Epidemiology Medicine, p.327-47
- Gates (2001) Am Fam Physician 63(3):513-22 [PubMed]
- MacLean (1996) Med Clin North Am 80(1):1-14 [PubMed]
- Nielsen (1999) Med Clin North Am 83(6):1323-37 [PubMed]