Lecture 2: Diagnostic Testing: Sensitivity and Specificity well answered to pass

Lecture 2: Diagnostic Testing:
Sensitivity and Specificity well
answered to pass

Diagnostic sensitivity - ANS ✔-Different from Analytic sensitity



Analytic sensitivity - ANS ✔The smallest amount of a substance in a sample that can accurately
be measured by an assay.



DIAGNOSTIC SENSITIVITY - ANS ✔-Probability of a POSITIVE test in an animal KNOWN to HAVE
the DZ+



the proportion of animals that test Positive out of a number of animals known to have the DZ



conceptual definition



10 Diseased (+) Cows



-after test, you find that

8 cows have (+) test (True positives) and

2 cows have (-) test (False Negatives )



What is the sensitivity ? - ANS ✔Definition states it is the probability of a positive test in an
animal KNOWN to have DZ(+)



So take 8(+)/10 (total pop)=80%

, Mathematical Definition of Sensitivity (formula) - ANS ✔Sensitivity TP/(TP + FN)



Math. Def. Of Sensitivity with Cow example - ANS ✔TP(8)/(TP(8)+FN(2)=0.80=80%



Specificity - ANS ✔-the probability of a NEGATIVE test in an animal known to NOT have the DZ(-)



-the proportion of animals that test negative out of a number of animals known to NOT have
the DZ(-)



conceptual definition: Specificity



10 cows Known NOT to have DZ



-After test :

2 test positive (False positive)

8 test negative (True Neg)



-What is Specificity? - ANS ✔Specificity is TN/(TN+FP)

=8/10= 80%



Mathematical Definition: Specificity - ANS ✔Specificity =TN/(FP+TN)



Cow example for Specificity - ANS ✔Specificity=TN(8)/ (TN(8) + FN(2)=0.80=80%



Basic Example: True Dz Prevalence =50% - ANS ✔TP=40