Diagnostic Tests

Question 1

Using the table, what is the sensitivity/specificity/overall accuracy/PPV/NPV equations? Positive likelihood ratio, negative likelihood ratio

                               Has diz.                 No diz Test Positive.                   A.                         B.                  (A+B)

Test Neg. C. D. (C+D)
(A+c). (B+d)

Answer 1

Sensitivity: a/(a+c)

Specificity d/(b+d)

Overall accurary: (a+d)/(A+b+c+d)

PPV: a/(a+b)

NPV: d/(c+d)

PLR: Sensitivity/ (1-specificity)

NLR: 1-sensitivity/(specificity)

Question 2

What is the positive predictive value of a test? Negative predictive value?

Answer 2

PPV -> probability of having disease, given a positive test result

NPV -> Probability of not having diz, given a neg test result

Question 3

What can we infer if the LR>10 or

Answer 3

Large and conclusive changes from pretest to posttest probability

Question 4

What is a likelihood ratio defined as?

Answer 4

Probability that test result in people with disease divided by probability of the result in people w/o disease.