Question

9. A new assay is used to test 120 samples from patients with a clinically confirmed diagnosis of the relevant infection and 50 samples from healthy control subjects. The test results were the infected patients and positive for 10 of the healthy controls. positive for 90 of What is the sensitivity of the assay? A. 57% B. 75% C. 80% D. 90% Using the narrative of question 9, calculate the assay's specificity A. 57% B. 75% C. 80% D. 90% 10. How should a 1:50 dilution be made if the final volume needed is 10 mL? A. 0.1 mL of serum and 9.9 mL of diluent B. 0.2 mL of serum and 9.8 mL of diluent C. 0.2 mL of serum and 10.0 mL of diluent D.0.5 mL of serum and 9.5 mL of diluent

Answer 1

9.

To calculate sensitivity and specificity, we need to construct 2x2 contingency table.

From the data given above, the table as below

	Has disease	Healthy controls	Total
Positive	90(a)	10(b)	100
Negative	30(c)	40(d)	70
Total	120	50	170

Sensitivity formula = a/a+c ( True positive÷ true positive + true negative).

=90/90+30

=90/120

=0.75

In percentage sensitivity=0.75×100

=75%

Answer is B.75%

Specificity formula=d/d+b( True negative÷True negative+false positive

=40/40+10

=40/50

=0.8

In percentage specificity=0.8×100

=80%.

Answer is C.80%

10.

1:50 dilution means 0.02/ml

For 10ml=10×0.02

=0.2ml of solute with remaining 9.8 ml diluent

Answer is B.0.2ml of serum and 9.8 ml of diluent