Epi practicals - 12 April 2021

Epi practicals

12 April 2021

Is this test useful

Practical - HIV

• Q1

	With disease	Without disease
test positive	152	20
test negative	8	980

• Q2
  • Sensitivity=[math]\displaystyle{ \frac{152}{160} = 0.95 }[/math]
  • Specificity=[math]\displaystyle{ \frac{980}{1000} = 0.98 }[/math]

• Q3

a)

	With disease	Without disease
test positive	38	1999.2
test negative	2	97960.8
sum	40	99,960

• Positive predictive value=[math]\displaystyle{ \frac{38}{38+1999.2}=0.0187 }[/math]
• Negative predictive value=[math]\displaystyle{ \frac{97960.8}{2+97960.8}=0.999 }[/math]

b)

	With disease	Without disease
test positive	316.35	1999.2
test negative	13.34	653.66
sum	333	667

• Positive predictive value=[math]\displaystyle{ \frac{316.35}{316.35+13.34}=0.959 }[/math]
• Negative predictive value=[math]\displaystyle{ \frac{653.66}{1999.2+653.66}=0.246 }[/math]

• Q4

To have high sensitivity is more important, because testing blood donor is a screening test and false-negative has to be excluded as much as possible.

• Q5

We need to calculate PPV and show the director how much false-positive donors arise.

• Q6

We should advise the director that donors should be informed to proceed to an additional confirmation test, not just be informed simple positive result.