Sensitivity and Specificity Calculator
Find a test's sensitivity and specificity.
Sensitivity catches true positives; specificity correctly rules out negatives.
How the Math Works
Sensitivity and specificity are fundamental metrics for evaluating the performance of diagnostic tests. Sensitivity, calculated as TP/(TP+FN), measures the proportion of actual positive cases that the test correctly identifies - essentially how good the test is at detecting true conditions when they are present. Specificity, calculated as TN/(TN+FP), measures the proportion of actual negative cases that the test correctly identifies - how well the test avoids false alarms. Together, these metrics provide a comprehensive view of a test's accuracy from both detection and confirmation perspectives.
Practical Applications
To use this calculator, input the four cardinal values from your 2x2 contingency table: True Positives (correctly identified cases), True Negatives (correctly identified non-cases), False Positives (healthy people incorrectly flagged), and False Negatives (sick people missed by the test). These values typically emerge from clinical trials or validation studies where your test results are compared against a gold standard diagnosis. The calculator will instantly compute both sensitivity and specificity, allowing you to quickly assess your test's reliability across different populations and scenarios without manual calculations.
Day-to-Day Use
Understanding these metrics empowers better health decisions in everyday life. When evaluating medical tests for yourself or loved ones, knowing sensitivity helps you understand the risk of false negatives - a highly sensitive test reduces the chance of missing a real condition. Specificity information protects against unnecessary anxiety and treatment from false positives. Whether it's a rapid COVID test, cancer screening, or any diagnostic tool, these calculations help you interpret results accurately and make informed healthcare choices with confidence.
Worked example
TP 90, FN 10, TN 80, FP 20 → sensitivity 90%, specificity 80%.
FAQ
Which matters more?
Screening favors high sensitivity; confirmation favors high specificity.