Blood banks will shortly start to screen all donors for NANB hepatitis

Question

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

Anu26 · Accepted Answer

Meaning of the question :

Let there be 100 people(all prospective blood donors) -> so 5 people will be caught in the new test.

2/3 * (people carrying nanb) = missed

therefore 1/3 * (people carrying nanb) = those that were caught = 5

therefore, people carrying nanb = 5*3 = 15

missed people = 10 (15-5) -> this is 10% of the prospective donor and the conclusion that they will still supply contaminated blood

Conclusion : 10% of actual donors will still supply NANB-contaminated blood

Now if donors carrying nanb carry other infections for which tests are routinely performed -> then the number of people carrying

nanb (with other infection) will be caught and will be less in number.

Thus, 2/3 * (people carrying nanb) -> will be less -> those missed will be less -> then we cannot claim that 10% of the donors will

still supply contaminated blood.

KarishmaB · Answer

Screening for NANB will start.
5% of prospective donors will be disqualified. (So if 100 people come to donate, only 95 will be allowed after NANB screening because 5 will have NANB).
But only 1/3rd will be caught and 2/3rd will still be missed. So these 5 make up only 1/3rd of total who carry NANB. So another 10 will be there carrying NANB but they will be missed.

Conclusion: About 10 percent of actual donors will still supply NANB-contaminated blood.

10 out of 95 allowed donors will have NANB so that's 'about 10%'. Looks right. Now the gap is will all these 95 supply blood i.e. will all of them be allowed to supply blood? For our conclusion, we are assuming that all these 95 will supply blood. That NANB test was the only hurdle they needed to cross to become actual donors.

(A) Donors carrying NANB hepatitis do not, in a large percentage of cases, carry other infections for which reliable screening tests are routinely performed.

Correct. We are assuming that no other test will disqualify many NANB carriers. What if NANB carriers usually carry other infections too which are tested for too? Then of these 10, perhaps another 8 would be disqualified because of other associated infections. So negating this breaks our conclusion.

(B) Donors carrying NANB hepatitis do not, in a large percentage of cases, develop the disease themselves at any point.

Irrelevant.

(C) The estimate of the number of donors who would be disqualified by tests for NANB hepatitis is an underestimate.

The argument takes the 1/3rd number to be accurate.

(D) The incidence of NANB hepatitis is lower among the potential blood donors than it is in the population at large.

No such comparison in the argument.

(E) The donors who will still supply NANB-contaminated blood will donate blood at the average frequency for all donors

We are talking about the donor numbers only, not the units donated and frequency of donation by each donor.

Answer (A)

boeinz · Answer

Tough one.

My explanation:

If NANB carries other infections which can be tested true positive (or reliable as stated in Option A), then the chance of detecting NANB will be higher. However, Option A states that this is not the case. Hence the 2/3 of NANB will still be missed and this figure (2/3) has to be taken as accurate. Thus its a necessary assumption.

ykaiim · Answer

Hi,

I solved this question with a different approach. I hope you will find it useful:

The premises are all seemed peculiar to me. But, I used %age and Number to solve this.

Conclusion is on ACTUAL 10% donors, which is nowhere mentioned in the argument. So, we need to look for following as per CR Bible:
1. Options which have ACTUAL keyword.
2. Options involveing %age instead of numbers, as we are given %ages only. So, choice with numbers will be Incorrect.
3. There seems to logical gaps in the argument and the author mentioned strong words to indicate that his reasoning is air-tight, which points to a DEFENDER assumption case. So, look for negative answer choices, which involve some defending language.

subhashghosh · Answer

Answer - A) Donors carrying NANB hepatitis do not, in a large percentage of cases, carry other infections for which reliable screening tests are routinely performed

So they'll escape the screening here, and the other screenings also, hence the number of infected donors who did not get filtered out does not change.

Say there are 15% donors affected, so 2/3 * 15 escape, hence 10% remain, they don't get caught in any other test so the %age is constant.

sowragu · Answer

Derived 'A' through POE.

Understanding of the passage.
P1 - Screening is happening.
P2 - Able to restrict only 5% out of 15%
C1 - Still 10% of ppl r giving the contaminated blood.

Assumption made - Some issue is there bcos of transfering this contaminated blood, Hence screening is happening in all the blood donors.

B - Donors carrying NANB hepatitis do not, in a large percentage of cases, develop the disease themselves at any point.   The information provided is not creating any link between the premise and conclusion. Also, if its not going to have any effect or creating any disease then why the screening is happening. 
(C) The estimate of the number of donors who would be disqualified by tests for NANB hepatitis is an underestimate. -   The statement has been already stated in the main Argument. Only 1/3rd was being identified.  
(D) The incidence of NANB hepatitis is lower among the potential blood donors than it is in the population at large. -   Complete Out of scope. Blood Donor Vs Total Population 
(E) The donors who will still supply NANB-contaminated blood will donate blood at the average frequency for all donors   Again its a statement or an information which no way supports the argument. Its a mere inforation. What ever frequecny they are giving it doesnt support the Conclusion made

So Finally A. A is ok with the pre assumption made during reading the argument. We are only checking for NANB, what if any other contamination is there? Through POE and pre assumption i reached A.

A is better choice among the 5.

HardWorkBeatsAll · Answer

I initially replied (E) incorrectly. Here's the explanation of why it is (A) -

Great question. Thanks for posting.

pkm9995 · Answer

It is already explained in the passage that 2/3rd of the NANB donors will not be detected.That means the current tests available for the NANB infection is not flawless. So the only chance is that,for NANB to be detected, they should have some other infectious disease(for which a flawless test is available) which occur along with NANB so that detection of the other disease will lead to elimination of NANB donor.This is what the logic given in option A.

gmatexam439 · Answer

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. - Correct. If these people have other diseases that are easily identifiable then they will be barred from blood donation.

B. Donors carrying NANB hepatitis do not, in a large percentage of cases, develop the disease themselves at any point. - Whether they develop the diseases is out of scope because having NANB virus will make them ineligible for blood donation, if caught in the test.

C. The estimate of the number of donors who would be disqualified by tests for NANB hepatitis is an underestimate. - Let it be an underestimation for we know 10% infected people will donate blood.

D. The incidence of NANB hepatitis is lower among the potential blood donors than it is in the population at large. - Out of scope

E. The donors who will still supply NANB-contaminated blood will donate blood at the average frequency for all donors - Still it doesn't clear whether 10% will donate or not.

Leo8 · Answer

" 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. "

Isn't the correct answer choice attacking the given premise. we are given that 2/3rd will be missed. How can we attack the given fact in the argument.

A. Donors carrying NANB hepatitis do not, in a large percentage of cases, carry other infections for which reliable screening tests are routinely performed.

if this is true, our premise doesn't stand.

I was actually hoping to see the link between donors and actual donors.

DAVEexamPAL · Answer

Leo8  it doesn't contradict our premise. We are asked which answer strengthens the premise that 2/3 of NANB donors will not be disqualified. One thing that is necessary for this is that those 2/3 won't be disqualified for any other reason - which is exactly what A tells us. 
Is this clear, or still confusing? Why do you think the premise doesn't stand?

DAVEexamPAL · Answer

Logically, we are given an assumption (the test will miss 2/3 of NANB donors) and a conclusion (2/3 of NANB donors, or 10% of all donors, will not be disqualified). But notice this assumes those infected won't be disqualified for any OTHER reason than NANB either - which is what A suggests.

By process of elimination:
A - Yes! this means if they aren't detected for NANb, they won't be detected for anything else. 
B - irrelevant
C - this contradicts the argument, it doesn't underline it 
D - not relevant: the stats we were given are about the potential donors, not the population at large
E - we don't know anything about the average frequency of donors, so this is just a distraction.

manasveek · Answer

the way i understood this argument is,
Considering sample size of 60 people who are donating blood.
among whom 5% disqualified because they have NAMB in their blood i.e. 3 are disqualified.
Further argument says, screening misses 2/3rd means it has caught 1/3rd of NAMB cases (1/3*x=3)
i.e. Total NAMB cases are 9 and 6 are missed cases.

6 are the people who have passed the screening despite having NAMB.
So conclusion correctly says 10% of 60(Total) i.e 6 will supply contaminated blood.

We want to break this conclusion by negating options.
option A on negation says- Donors carrying NANB hepatitis carry other infections for which reliable screening tests are routinely performed.
Means out of 6 who managed to get through new screening will fail some other screening like of other blood test criteria and that number 10% (say 6) will be reduced.
And few people despite having NAMB and having passed NAMB screening will go ahead with donation.
As this reasoning breaks conclusion. It must be the right choice.

warrior1991 · Answer

We are asked that what has been assumed.

This is very interesting choice.  
Read carefully.  Negate  this choice.

Hence A is correct.

This is a really good question.

teaserbae · Answer

AjiteshArun 
I choose B.
I interpreted B as if the NANB hepatitis develop of its own then there might be increase in the number of donors having NANB hepatitis there by weakening the conclusion that only 10% will be left.

AjiteshArun · Answer

The conclusion is:

Therefore, about 10 percent of actual donors will still supply NANB-contaminated blood.

Option A :  Donors carrying NANB hepatitis do not, in a large percentage of cases, carry other infections for which reliable screening tests are routinely performed.

The argument says that because the NANB screening misses 2 out of every 3 people with NANB-contaminated blood, 10% of the donors will continue to supply NANB-contaminated blood. This conclusion does not take into account the possibility that there could be other ( reliable ) screening processes for other problems.

If we apply negation, we see that if people with NANB-contaminated blood  do  have other problems that reliable screening methods can detect, then the conclusion that 10% of donors will donate NANB-contaminated blood is weakened, as these people will get "screened out" by these other tests.

Option B :  Donors carrying NANB hepatitis do not, in a large percentage of cases, develop the disease themselves at any point.

This option basically says that for the conclusion to be true, donors with NANB-contaminated blood should never get the disease at any point in their lives.

I think the most important thing to remember here is that this is an  assumption  question, and not a general strengthen question. In assumption questions, we need to pick an option that, given the logic of the argument, the argument  needs  in order to get to its conclusion. This argument does not  need  donors with NANB-contaminated blood to be  free  or  not free  of the actual disease  at any point . Just the fact that these donors have NANB-contaminated  blood  is enough.

You might be looking at the possibility that NANB hepatitis is infectious. However, whether it is infectious or not is already "factored in". That is, option B does not involve a change in the nature of the disease from non-infectious to infectious.

dcummins · Answer

The argument is that ~10% of actual donors will supply contaminated blood.
This is supported by the fact that even though up to 5% of all prospective donors are eliminated from donating, still 2/3rds of donors carrying NANB are missed. 
Yes, we can waste time doing math but that doesn't change much really:  1/3*X donating population is detected = 5 therefore x (donation population = 15%).

The question AND GAP between the evidence and conclusion is WHY is there still an additional 5% of people going undetected and slipping through to the actual donator pool?
(A) Donors carrying NANB hepatitis do not, in a large percentage of cases, carry other infections for which reliable screening tests are routinely performed.

A  must be true. Our expectation, for the conclusion to be true, is that 5% of people will slip through the tests performed. A thus denies the possibility that this WONT be the case by stating that donors WONT get picked up by other more reliably screening tests for other infections they may be carrying.

A defends the argument. It denies the possibility that the argument WONT hold.

(B) Donors carrying NANB hepatitis do not, in a large percentage of cases, develop the disease themselves at any point.

B is incorrect because even if the donors DO develop the disease themselves it's irrelevant to the pre-screening detection and thus argument at hand.

(C) The estimate of the number of donors who would be disqualified by tests for NANB hepatitis is an underestimate.

Even if the estimate is an underestimate, say the estimate is 7.5%. This doesn't change the fact some donors will slip through, so we need to understand the gap between the methods of detection and WHY they are slipping through.

(D) The incidence of NANB hepatitis is lower among the potential blood donors than it is in the population at large.

Again this doesn't change anything. The argument tries to fool the reader with numbers, so D attempts to make a ploy at saying the incidence is lower. This does not change the premise that 5% of potential donors are detected and that 10% still manage to slip through.

(E) The donors who will still supply NANB-contaminated blood will donate blood at the average frequency for all donors

Frequency of donation is irrelevant to the % of infected donors slipping through.

gagan0303 · Answer

GMATNinja  please help on this one.

mSKR · Answer

My 2 cents:

Argument: Donors(100) --- > Reject 5% who had NANB ; 95% : 10% have still NANB ----- > still 10% supply NANB contaminated blood

Add below information in above equation
In argument: Blood banks will shortly start to screen all donors
OPTION A : further donors will no more be rejected
i.e.: Donors -- > TESTING/QUALIFICATION -- > Actual DONATE

==> Donors(100) --- > Reject 5% who had NANB ; 95% : 10% have still NANB ----- >  OPTION A  --- > still 10% supply NANB contaminated blood

Why not B? Because even develop, we can’t identify it

Why not C? So it means actual disqualification will be more? But conclusion is based on percentages .

Why not D? But how can actual donors be more than population at large? Even many , how does it matter? We have percentage calculations given .

Why not E? Because we are talking of donors not frequency of per donor.

Blood banks will shortly start to screen all donors for NANB hepatitis

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Blood banks will shortly start to screen all donors for NANB hepatitis

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