In tests for Feline Leukemia Virus (FeLV), a serious disease : GMAT Critical Reasoning (CR)
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# In tests for Feline Leukemia Virus (FeLV), a serious disease

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In tests for Feline Leukemia Virus (FeLV), a serious disease [#permalink]

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10 Aug 2011, 01:39
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In tests for Feline Leukemia Virus (FeLV), a serious disease of domestic cats, a false positive result indicates that a cat has FeLV, when in fact, it does not; a false negative result indicates that a cat does not have FeLV when, in fact, it does. To detect FeLV most accurately, veterinarians should use the laboratory test that has the lowest proportion of false negative results.

Which of the following, if true, gives the most support to the recommendation above?

A-A certain proportion of results are inconclusive no matter which laboratory test is used.

B-There is no known cure for FeLV, although some chemotherapeutic agents may produce a temporary remission and some antiviral agents may reduce the amount of virus present in infected cats.

C-Cats do not readily submit to having their blood drawn for a test.

D-Upon receiving a positive test result, veterinarians often submit a second sample to be retested for confirmation.

E- All laboratory tests to detect FeLV have the same rate of false positive results.

OA is
[Reveal] Spoiler:
E

My question is this.....kaplan explains that D is irrelevant and costly. However, if the the Veteranarians agree to only using tests with the least false negatives , then the proportion of false positives will increase correct? Either way there will be inaccurate test results, its just a matter of whether they are more dangerous (false negative) or less dangerous (false positive). So wouldnt it be better to have false positives and then re take the test?
[Reveal] Spoiler: OA
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10 Aug 2011, 03:22
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In tests for Feline Leukemia Virus (FeLV), a serious disease of domestic cats, a false positive result indicates that a cat has FeLV, when in fact, it does not; a false negative result indicates that a cat does not have FeLV when, in fact, it does. To detect FeLV most accurately, veterinarians should use the laboratory test that has the lowest proportion of false negative results.

Which of the following, if true, gives the most support to the recommendation above?

E- All laboratory tests to detect FeLV have the same rate of false positive results.

This one is simply a matter of there being 2 tests. Event Neg and Event Pos. So in the case of E is is saying that NO MATTER WHAT all laboratory tests to detect FeLV will have the same rate of false positive. Which means that you're going to want to pick the lab test that has the lowest proportion of negative results and therefore it supports the theory. so E is the correct answer.

To make it easier to understand, you obviously want the least number of errors so lets take 5 random tests:
-------------Pos Errors----Neg Errors-------Total Errors
Lab test 1-------3-------------2----------------5
Lab test 2-------3-------------3----------------6
Lab test 3-------3-------------4----------------7
Lab test 4-------3-------------1----------------4
Lab test 5-------3-------------2----------------5

Therefore it doesnt matter what the proportion of Pos errors is, the total number of errors goes down. And for the record with False Pos it tells them that they have FeLV when they don't so they would have to take the test again to confirm because it would be costly for treatment just as they would take the False Neg again to make sure the cat is ok. Either way they would take the test to confirm a second time there is no difference between two false.
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10 Aug 2011, 05:28
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nphelan wrote:
In tests for Feline Leukemia Virus (FeLV), a serious disease of domestic cats, a false positive result indicates that a cat has FeLV, when in fact, it does not; a false negative result indicates that a cat does not have FeLV when, in fact, it does. To detect FeLV most accurately, veterinarians should use the laboratory test that has the lowest proportion of false negative results.

Which of the following, if true, gives the most support to the recommendation above?

E- All laboratory tests to detect FeLV have the same rate of false positive results.

This one is simply a matter of there being 2 tests. Event Neg and Event Pos. So in the case of E is is saying that NO MATTER WHAT all laboratory tests to detect FeLV will have the same rate of false positive. Which means that you're going to want to pick the lab test that has the lowest proportion of negative results and therefore it supports the theory. so E is the correct answer.

To make it easier to understand, you obviously want the least number of errors so lets take 5 random tests:
-------------Pos Errors----Neg Errors-------Total Errors
Lab test 1-------3-------------2----------------5
Lab test 2-------3-------------3----------------6
Lab test 3-------3-------------4----------------7
Lab test 4-------3-------------1----------------4
Lab test 5-------3-------------2----------------5

Therefore it doesnt matter what the proportion of Pos errors is, the total number of errors goes down. And for the record with False Pos it tells them that they have FeLV when they don't so they would have to take the test again to confirm because it would be costly for treatment just as they would take the False Neg again to make sure the cat is ok. Either way they would take the test to confirm a second time there is no difference between two false.

I narrowed my choices down to D and E but picked D....thanks for the great explanation.
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10 Aug 2011, 05:46
+1 for E
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10 Aug 2011, 09:19
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10 Aug 2011, 11:00
Good explanations i kudos but im on a mobile phone

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Re: In tests for Feline Leukemia Virus (FeLV), a serious disease [#permalink]

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26 Feb 2012, 05:51
There are 2 ways a report of a lab can be questioned:
based on its false -ve rate & fase +ve rate.

If all labs give same result for +ve rate, obviously we need to depend on false -ve rate. Hence E is correct.

As per D - no matter what the first report says, doctors are going to submit for second test for confirmation. What if the second result contradicts with the first one? There is no answer for this question and hence D is not correct.
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Re: In tests for Feline Leukemia Virus (FeLV), a serious disease [#permalink]

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27 Feb 2012, 23:25
Choice E is the correct one.
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Re: In tests for Feline Leukemia Virus (FeLV), a serious disease [#permalink]

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07 Jan 2013, 19:57
Argument states two issues - False positive and False negative results of tests. However the author suggests one issue over other (Say issue 2 over issue 1). We need to find out why Issue2 is more significant and Issue1 can be less of a priority.

Choice (E) correctly supports author's recommendation. That Issue 1 (false positive ) tests have same accuracy statistics, thus he recommends addressing issue2 (false negative tests)
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Re: In tests for Feline Leukemia Virus (FeLV), a serious disease [#permalink]

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11 May 2014, 21:22
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Re: In tests for Feline Leukemia Virus (FeLV), a serious disease [#permalink]

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18 Sep 2015, 22:35
Hello from the GMAT Club VerbalBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: In tests for Feline Leukemia Virus (FeLV), a serious disease [#permalink]

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16 Oct 2015, 22:57
I could nt understand this...Can anyone elaborate?
Re: In tests for Feline Leukemia Virus (FeLV), a serious disease   [#permalink] 16 Oct 2015, 22:57
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