Question

Two pediatricians want to investigate a new laboratory test that investigates streptococcal infections. Dr. Kidd uses the standard culture test, which has a sensitivity of 90% and a specificity of 96%. Dr. Childs uses the new test, which is 96% sensitive and 96% specific.

A) For children deciding to use both tests SEQUENTIALLY, first Dr. Kidd’s then Dr. Childs’s, what is the net sensitivity? What is the net specificity?

(hint: to be included in test B (by Dr. Child), children must have first identified as positive under Dr. Kidd’s test)

Answer 1

Here given

Dr Kidd's test sensitivity =90% and specificity =96%

Dr.childs test sensitivity=96% and specificity=96%

NET SENSITIVITY

(#) When two tests are used simultaneously, disease positives are
defined as those who test positive by either one test or by
both tests
(#) We use the addition rule of probability to calculate the net
sensitivity

Therefore net sensitivity = sens 1 + sens 2 – (sens 1 x sens 2)

= 0.90 + 0.96 - (0.90 × 0.96)

= 0.996. [=99.6%]

NET SPECIFICITY

(#) When two tests are used simultaneously, disease negatives
are defined as those who test negative by both tests
(#) We use the multiplication rule of probability to calculate the
net specificity

Therefore net specificity = specificity test 1 × specificity test 2

= 0.96 × 0.96

= 0.9216 [92.16%]