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Sensitivity & Specificity Calculator

Enter confusion matrix counts to evaluate diagnostic test characteristics and interpret likelihood ratios.

Sensitivity

95.00%

True positive rate

Specificity

92.31%

True negative rate

PPV

86.36%

Positive predictive value

NPV

97.30%

Negative predictive value

Accuracy

93.22%

(TP + TN) / Total

Prevalence

33.90%

(TP + FN) / Total

Likelihood Ratios

LR+ = 12.35
LR− = 0.05

False positive rate: 7.69% • False negative rate: 5.00%

How to Use This Calculator

  1. Supply confusion matrix counts: true/false positives and negatives.
  2. Review sensitivity/specificity for intrinsic test accuracy.
  3. Check predictive values, which depend on disease prevalence.
  4. Use likelihood ratios to update probabilities with Bayes’ theorem.

Formula

Sensitivity = TP / (TP + FN)

Specificity = TN / (TN + FP)

PPV = TP / (TP + FP)

NPV = TN / (TN + FN)

LR+ = Sensitivity / (1 − Specificity)

LR− = (1 − Sensitivity) / Specificity

Full Description

Sensitivity and specificity describe a test’s intrinsic ability to detect disease versus health. Predictive values reveal how test results translate into real-world probabilities, influenced by prevalence. Likelihood ratios bridge test results and Bayesian reasoning, powering post-test probability calculations.

This calculator is ideal for clinicians, epidemiologists, and students learning diagnostic testing concepts.

Frequently Asked Questions

Why do predictive values change with prevalence?

Prevalence influences the proportion of true positives/negatives in the population. Higher prevalence increases PPV and decreases NPV, and vice versa.

What if some counts are zero?

Zero counts can produce infinite likelihood ratios. Consider continuity corrections or exact statistical methods when sample sizes are small.

How is this different from accuracy?

Accuracy combines both true positives and negatives but can be misleading when classes are imbalanced. Sensitivity and specificity separate these effects.

How can I use likelihood ratios?

Multiply pre-test odds by LR+ or LR− to update disease probability. Use the post-test probability calculator to streamline this process.