Sensitivity and specificity of two tests used in parallel or series

Input Values


This utility calculates the overall sensitivity and specificity of the testing regimen when two tests of known sensitivity and specificity are used together, either in parallel or in series. Calculations assume that the two tests are independent, conditional on disease status (that is, sensitivity [specificity] for one test remains the same, regardless of the result of the other test.

Inputs required

  • Sensitivity and specificity for test 1; and
  • Sensitivity and specificity for test 2.


  • Sensitivity and specificity interpreted in series; and
  • Sensitivity and specificity interpreted in parallel.


Se(series) = Se1 x Se2
Se(parallel) = 1 - (1 - Se1) x (1 - Se2)
Sp(series) = 1 - (1 - Sp1) x (1 - Sp2)
Sp(parallel) = Sp1 x Sp2


Sergeant & Perkins, 2016. Epidemiology for Field Veterinarians: an Introduction. CABI, Wallingford, UK. pp 98-102.
Thrusfield, 1995, Veterinary Epidemiology, 2nd ed. Blackwell Science Ltd, Oxford, UK. pp 279-280.


Excel example
R function
Parallel versus Serial testing
Test sensitivities and specificities:
  Sensitivity Specificity


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