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# In testing for food allergies, a false positive result

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Re: In testing for food allergies, a false positive result  [#permalink]

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07 May 2015, 14:26
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In all CR questions like this, which recommend a certain 'policy' or 'approach', you must very clearly identify the goal of that policy or approach. The question says: "To most accurately determine food allergies a physician should use the test that gives the smallest percentage of false negative results." The red bit is all we care about in this question: using the test that is the most accurate. Any answer choice that is not about test accuracy is definitely wrong.

Using the test with the fewest false negatives sounds good if we want an accurate test, but what if that test has a lot of false positives? Then it might not be the most accurate test. But if all tests have the same proportion of false positives, the test with the fewest false negatives is the most accurate, which is why E is the correct answer.
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Re: In testing for food allergies, a false positive result  [#permalink]

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12 Jun 2015, 13:17
souvik101990 wrote:
In testing for food allergies, a false positive result occurs when a person is said to be allergic to a particular food when, in fact, he is not allergic to that food. A false negative result indicates that a person is not allergic to the food when, in fact, he is. To most accurately determine food allergies, a physician should use the test that gives the smallest percentage of false negative results because _________________________

A. some food allergies cause reactions severe enough to be life-threatening
B. none of the tests for food allergies have lasting side effects
C. in diagnosing food allergies it is important to be as thorough as possible, since most people with one known food allergy have other undiscovered food allergies
D. the proportion of tests that do not provide a clear result is the same for all tests of food allergies
E. all tests for food allergies have the same proportion of false positive results

The answer is clearly E. Imagine that a proportion of false positive results is 8 out of 10. Hence out of 10 people 8 are not allergic to food. Hence to maximize total number of people who are not allergic to food we should minimize number of people who are allergic to food. This is what stimulus says. Hope it is clear!
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Re: In testing for food allergies, a false positive result  [#permalink]

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31 Oct 2015, 08:53
In testing for food allergies, a false positive result occurs when a person is said to be allergic to a particular food when, in fact, he is not allergic to that food. A false negative result indicates that a person is not allergic to the food when, in fact, he is. To most accurately determine food allergies, a physician should use the test that gives the smallest percentage of false negative results because _________________________

A. some food allergies cause reactions severe enough to be life-threatening..............OFS
B. none of the tests for food allergies have lasting side effects...............OFS
C. in diagnosing food allergies it is important to be as thorough as possible, since most people with one known food allergy have other undiscovered food allergies................OFS
D. the proportion of tests that do not provide a clear result is the same for all tests of food allergies............OFS
E. all tests for food allergies have the same proportion of false positive results.............address why don't need to bother about this section of results

I misread the question and landed upon option C at first.
Then I realized that E is the correct answer after re-reading the question.
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Re: In testing for food allergies, a false positive result  [#permalink]

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25 Apr 2016, 10:14
I made a mistake by choosing A. Again I realized what my mistake was. Let us break down the premise and the conclusion
A test can give both false positive and false negative.
Conclusion - Selecting a test based purely on the min false negative will be the most accurate.
Here the argument is not about the impact of not doing so, but the objective is to purely get the most accurate test. The gap in the argument is well what if the most accurate test in terms of false negative scores poorly on false positive. The answer choice E addresses that and therefore is the right answer
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Re: In testing for food allergies, a false positive result  [#permalink]

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04 May 2016, 19:01
souvik101990 wrote:
In testing for food allergies, a false positive result occurs when a person is said to be allergic to a particular food when, in fact, he is not allergic to that food. A false negative result indicates that a person is not allergic to the food when, in fact, he is. To most accurately determine food allergies, a physician should use the test that gives the smallest percentage of false negative results because _________________________

A. some food allergies cause reactions severe enough to be life-threatening
B. none of the tests for food allergies have lasting side effects
C. in diagnosing food allergies it is important to be as thorough as possible, since most people with one known food allergy have other undiscovered food allergies
D. the proportion of tests that do not provide a clear result is the same for all tests of food allergies
E. all tests for food allergies have the same proportion of false positive results

oh man...i got some food allergy and it is very frustrating to identify to which product you are actually allergic...
we need an answer choice that would make false negative better than false positive.
A is out right away
B side effects are out of scope
C this one seems to favour false positive - no
D basically says that false negative = false positive so no
E all tests have same proportion of false positive - thus, false positive is not a good option.

E for me.
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Re: In testing for food allergies, a false positive result  [#permalink]

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10 Aug 2016, 01:53
In testing for food allergies, a false positive result occurs when a person is said to be allergic to a particular food when, in fact, they are not allergic to that food. A false negative result indicates that a person is not allergic to the food when, in fact, they are. To most accurately determine food allergies, a physician should use the test that gives the smallest percentage of false negative results.

Goal is to determine accurately food allergies.
Two types of tests are there :
1> that measure false positive results more than false -ve results
2> that measure false -ve results more than false +ve results

A physician should choose 1st one rather than 2nd to determine accurately food allergies. . Why?
Prethinking

1> Test that measure false positive results more than false -ve results, overall accuracy rate is more than the 2nd one.

Which of the following, if true, most supports the recommendation that is given above?

A. Some food allergies cause reactions severe enough to be life-threatening. > doesn't answer our dilemma over +ve -Ve
B. None of the tests for food allergies have lasting side effects. same
C. In diagnosing food allergies it is important to be as thorough as possible, since most people with one known food allergy have other undiscovered food allergies.

D. The proportion of tests that do not provide a clear result is the same for all tests of food allergies

E. All tests for food allergies have the same proportion of false positive results > if all test have same false positive result, one variable down. only -ve we are left to.
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Re: In testing for food allergies, a false positive result occurs when a p  [#permalink]

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19 Mar 2017, 05:02
Why is it E and not A?

Posted from my mobile device
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Re: In testing for food allergies, a false positive result occurs when a p  [#permalink]

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19 Mar 2017, 15:46
Please, specify the source of this question.
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Re: In testing for food allergies, a false positive result occurs when a p  [#permalink]

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21 Mar 2017, 12:35
why is the answer not c and a some one can please throw some light on this one.. thanks
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In testing for food allergies, a false positive result occurs when a p  [#permalink]

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28 Mar 2017, 23:22
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nailin16 wrote:
Why is it E and not A?

Posted from my mobile device

Between E & A , E is a shell game. It seems to be the right answer , but it is not.

Let me break down the argument.

Tests for allergies have 2 problems (errors)
1. False positive, which means the person is not allergic , but the test shows positive result.
2. False negative, which means the person is allergic , but the test shows negative results .

The conclusion says that, in order to determine food allergy , the doctor must depend on the 2nd point above.

A. some food allergies cause reactions severe enough to be life-threatening
- If some food allergies can become life-threatening, does that help to prove the conclusion . No, because the severity of the food allergy is simply out of scope of this argument.

E. all tests for food allergies have the same proportion of false positive results
- If there are two types of error of the test as stated above, and the percentage of errors of type 1 are same across all the test cases, then then type 2 is the determining factor.
Let's say for all the test cases 100 = 78 gives the right results + errors (22)
We know errors are of 2 types. As the percentage of one type of error is always same, the other type (2) becomes the determining factor.

This is quite a detailed analysis , which is not possible during the actual exam. I wrote all these only to make you understand.
Instead I relied more on negating the options out of A & E. Carefully reading the argument shows that A is out of scope.
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Re: In testing for food allergies, a false positive result  [#permalink]

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28 Jul 2017, 08:20
Merged topics. Please, search before posting questions!
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Re: In testing for food allergies, a false positive result  [#permalink]

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02 Aug 2017, 15:10
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There are some great explanations on here for why E is correct, so kudos to everyone who has posted on that!

And then to fully answer the recurring of question of "why is it E and not A?" let me throw this out:

When you're working with a plan/strategy problem (as opposed to a classic "argument"), the goal/objective plays the role of the conclusion. And as always with Strengthen/Weaken, the specific conclusion is absolutely crucial! The same, then, is true of the objective. Here, look at what the objective is:

"To most accurately determine food allergies."

Choice A doesn't tell you why focusing on false negatives leads to increased accuracy. Choice A is all about safety/severity - it supports a different conclusion/objective, to be as safe as possible. Which...I like telling my classes when we do this one (and at least half of people pick A every time), if you pick A, you're a really good person and will be a really good parent. Of course any good person would want to minimize the number of false negatives, because if someone thinks that they're not allergic but it turns out that they are, then they may very well eat something that could seriously hurt or even kill them. So you should absolutely in your heart and soul want to pick A for humanitarian reasons...but the goal as stated in the argument isn't safety, it's accuracy. And if the tests that reduce false negatives by 1%, in turn, increase false positives by 50%, then you haven't prioritized accuracy.

So that's the problem with A. It:

-Doesn't deal with the specific conclusion/objective, so it's incorrect.

-Is really tempting because the objective it leads to is one that your mind should naturally gravitate toward.

-Teaches a great lesson. The precise language in the conclusion (or objective) is absolutely crucial, so make sure that you read it carefully.

One more note on A - we like to call the device behind A "selling the wrong answer" through "mental inertia." If you have an interest in or some knowledge of a CR topic, it's even more important to be extra careful when reading the prompt/conclusion/objective because on those topics it's easier for the testmaker to satisfy that "ah, I like this answer" reaction with a wrong answer, because what it's satisfying is more related to your opinion or recollection. So if the topic matter speaks to you, remind yourself to slow down just a bit more so that you don't chase an answer that "feels good" but doesn't directly answer the question.
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Updated on: 07 Aug 2017, 05:06
Which of the following best completes the passage below?

In testing for food allergies, a false positive result occurs when a person is said to be allergic to a particular food when, in fact, he is not allergic to that food. A false negative result indicates that a person is not allergic to the food when, in fact, he is. To most accurately determine food allergies, a physician should use the test that gives the smallest percentage of false negative results because _______________.

(A) some food allergies cause reactions severe enough to be life-threatening
(B) none of the tests for food allergies have lasting side effects
(C) in diagnosing food allergies it is important to be as thorough as possible, since most people with one known food allergy have other undiscovered food allergies
(D) the proportion of tests that do not provide a clear result is the same for all tests of food allergies
(E) all tests for food allergies have the same proportion of false positive results”

Originally posted by Bounce1987 on 07 Aug 2017, 04:46.
Last edited by broall on 07 Aug 2017, 05:06, edited 1 time in total.
Merged topic. Please search before posting question.
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07 Aug 2017, 04:50
What would be the right methodology to untangle a critical reasoning question like this one?
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Re: In testing for food allergies, a false positive result  [#permalink]

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07 Aug 2017, 05:41
This question is almost an exact copy of an old OG question:

https://gmatclub.com/forum/in-tests-for ... 37758.html

The official version would be the more worthwhile one to study, if only because it is better written.
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Re: In testing for food allergies, a false positive result  [#permalink]

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18 Sep 2017, 17:45
In testing for food allergies, a false positive result occurs when a person is said to be allergic to a particular food when, in fact, they are not allergic to that food. A false negative result indicates that a person is not allergic to the food when, in fact, they are. To most accurately determine food allergies, a physician should use the test that gives the smallest percentage of false negative results.

Which of the following, if true, most supports the recommendation that is given above?

A. Some food allergies cause reactions severe enough to be life-threatening.
- not interested in the severities of "some" food allergies.

B. None of the tests for food allergies have lasting side effects.
- not interested in the side effects of food allergies

C. In diagnosing food allergies it is important to be as thorough as possible, since most people with one known food allergy have other undiscovered food allergies.
- not interested in "other undiscovered" food allergies people may have

D. The proportion of tests that do not provide a clear result is the same for all tests of food allergies
- how many different types of tests are we considering? plus, "clear result" is a little confusing -- why not just mention "a result"?

E. All tests for food allergies have the same proportion of false positive results
- correct as is. this would help us accurately determine food allergies.

Key: POE to easily elim A, B & C. Then you have to scrap it up between D & E.
> Helpful hint: reframe what the Conclusion is and what your goal is. You want to ACCURATELY determine a #. Anything that does not align with this is not addressing the Conclusion.

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Re: In testing for food allergies, a false positive result  [#permalink]

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24 Oct 2018, 06:23
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 testing for food allergies, a false positive result &nbs [#permalink] 24 Oct 2018, 06:23

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