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Diagnostic test evaluation and comparison

Sensitivity and specificity of two tests used in parallel or series

Test sensitivities and specificities

Test Number	Test Name	Sensitivity (Se)	Specificity (Sp)
1
2

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.

Input values

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

Outputs

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

Formulae

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

References

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.