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Sensitivity And Specificity Calculator

Work out sensitivity and specificity instantly with clear inputs, formula shown and shareable results.

About Sensitivity And Specificity Calculator

Sensitivity is the fraction of diseased people the test catches and specificity the fraction of healthy people it clears. Predictive values answer the patient's question instead, and they depend heavily on prevalence.

Formulas

Sensitivity and specificity

Sens = TP/(TP + FN), Spec = TN/(TN + FP)

Predictive values

PPV = TP/(TP + FP), NPV = TN/(TN + FN)

Worked example

With the default values below, Sensitivity And Specificity Calculator returns Sensitivity (true positive rate) of 0.90000000. Change any input above and every figure here is recalculated in your browser.

Inputs used

True positivesminimum 0
90
False negativesminimum 0
10
True negativesminimum 0
855
False positivesminimum 0
45

Results

Sensitivity (true positive rate)
0.90000000
Specificity (true negative rate)
0.95000000
Positive predictive value
0.66666667
Negative predictive value
0.98843931

Step by step

  1. 1Values used
  2. 2Sensitivity and specificity
  3. 3Predictive values
  4. 4Sensitivity (true positive rate)= 0.90000000
  5. 5Specificity (true negative rate)= 0.95000000
  6. 6Positive predictive value= 0.66666667
  7. 7Negative predictive value= 0.98843931

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 8 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

For 90 TP, 10 FN, 855 TN and 45 FP?

Sensitivity is 90% and specificity 95%, but the positive predictive value is only 66.7%.

Why is PPV lower than sensitivity?

Because the healthy group is nine times larger here, so its 5% false-positive rate contributes many of the positives.

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