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# Blood Banks

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Director
Joined: 05 Jan 2005
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29 Jun 2005, 07:48
Blood banks will shortly start to screen all donors for NANB hepatitis. Although the new screening tests are estimated to disqualify up to 5 percent of all prospective blood donors, they will still miss two-thirds of donors carrying NANB hepatitis. Therefore, about 10 percent of actual donors will still supply NANB-contaminated blood.

The argument above depends on which of the following assumptions?
(A) Donors carrying NANB hepatitis do not, in a large percentage of cases, carry other infections for which reliable screening tests are routinely performed.
(B) Donors carrying NANB hepatitis do not, in a large percentage of cases, develop the disease themselves at any point.
(C) The estimate of the number of donors who would be disqualified by tests for NANB hepatitis is an underestimate.
(D) The incidence of NANB hepatitis is lower among the potential blood donors than it is in the population at large.
(E) The donors who will still supply NANB-contaminated blood will donate blood at the average frequency for all donors.

I'm interested in your explanations please - I obviously know the OA.
If you have any questions
New!
Senior Manager
Joined: 06 Apr 2005
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29 Jun 2005, 08:34
This CR is tough. I will go with A.

Lets analyze the argument
Lets assume there are a 100 prospective donors. 5% of them will be disqualified as they carry the NANB virus. The tests will miss Two thirds of the donors having the NANB (1/3 = 5, so there are 15 donors with NANB, meaning 10 with NANB won't be disqualified). Therefore 10 percent of donors with NANB virus won't be detected.

if this 10% carried another infection, they would have been detected in other tests. Therefore this argument assumes that "Donors carrying NANB hepatitis do not, in a large percentage of cases, carry other infections for which reliable screening tests are routinely performed."

Phew... Sorry for the long boring explanation. Couldn't help it
Senior Manager
Joined: 30 May 2005
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29 Jun 2005, 08:44

This is because the statement assumes that those NANB carriers missed by the NANB filters are not trapped by other filters which they have to pass before becoming a donor. It either assumes that the missed NANB carriers pass the other reliable filters or there are no other filters.
Director
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30 Jun 2005, 00:21
OA is (A). i finally got it. thanks.
30 Jun 2005, 00:21
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