In tests for pironoma, a serious disease, a false positive result indi

Premise 1: a false positive result indicates that people have pironoma when, in fact, they do not;

Premise 2: a false negative result indicates that people do not have pironoma when, in fact, they do.

Conclusion: To detect pironoma most accurately, physicians should use the laboratory test that has the lowest proportion of
false positive results.

The conclusion that the author draws is unexpected because we should look for laboratories that have the lowest proportion of false negative results. However, the questions is asking for an answer choice that strengthens the argument.

Option E says that all the laboratories have the same proportion of false negative results. If all have the same proportion, then the one with the lowest proportion of false positive results would be the best.

Consider the following example

Height is the most important feature for a basketball player, whereas speed is the second one. However, Richard is the best player in his team because he is the fastest.

What would make this conclusion be properly drawn?

All the players in Richard's team have the same height.

This problem contains some great examples of one of the GMAT test writers' favorite tricks: answers that strengthen or weaken not the stated conclusion, but rather a related but different conclusion. This is why it's so crucial to precisely identify the stated conclusion on strengthen / weaken questions!

Note that the full conclusion is


We are trying to detect pironoma most accurately - we have no other goals here!

See any problems with this conclusion? To achieve the most accurate results, the conclusion says we should focus on minimizing false positives. But wait a minute, the passage discussed two sources of inaccuracies in these tests - false positives and false negatives. The conclusion does not address false negatives, so to strengthen we need a statement that does!

A) Side affects are certainly a real-world concern, but they are not discussed in the stated conclusion (or in the passage at all, for that matter!) Wrong.
B) Same problem as A). Wrong.
C) Again, early treatment is a real-world concern, but not a concern for this argument. Wrong.
D) Inconclusive results were not discussed as a source of inaccuracies in the passage. This is probably a mild strengthener, because it does eliminate one other concern (the conclusion narrows our concerns all the way down to just false positives). But since it does not address false negatives, we should be highly suspicious of this answer. Go ahead and read E), but this one is probably wrong.
E) Here we have our exact prediction. Correct.

Takeaways:

[•] Carefully note the exact wording of the conclusion.
[•] Don't be tempted by logical answers that are out of scope for the given argument.

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In other words,
X and Y are two scenarios/situations that affect a conclusion.

When can we say that the conclusion depends ONLY on how X varies?
=>Only when Y is constant or when it varies proportionately we can say that the conclusion entirely depends on how X varies.

Choosing Option E here.

Reasoning : am assuming each lab tests consists of false postive results,accurate results and false negative results. Providing treatment to a person not afflicted by the disease ( a false positive) may have serious side effects ,while in the other 2 cases- false negative and accurate,the treatment works in the person's favour.

So ,if all lab tests have the same proportion of false -ve results,it make sense to use the laboratory test that has the lowest proportion of false positive results for minimising the risk of any adverse side effects ,while maximising treatment benefit to the rest of the population.

In all CR questions one should always first understand the conclusion properly , and then focus on how the conclusion can be strengthened / weakened etc.
In strengthen questions we have to find a fact/premise that would reinforce the conclusion in hand.
To do this always prethink an answer that would do one of the above before moving on to the actual answer choices.
Lets take a look at this question

The conclusion here states that "To detect pironoma most accurately, physicians should use the laboratory test that has the lowest proportion of false positive results."
That means physicians are looking for tests that have the tests that detect that one has Pironoma but in actual one does not have it.
Just think for a second why would physicians use this test - maybe because lot of laboratory tests do not detect Pironoma but in actual people have it.
Keeping this in mind we look a the answer choices :

(A) The accepted treatment for pironoma does not have damaging side effects.
- Looks tempting , but focus more closely and you will see that it talks about treatment and not on the conclusion hence ruled out.
(B) The laboratory test that has the lowest proportion of false positive results causes the same
minor side effects as do the other laboratory tests used to detect pironoma.
- again irrelevant
(C) In treating pironoma patients, it is essential to begin treatment as early as possible, since
even a week of delay can result in loss of life.
- irrelevant - talks about treatment rather than detection
(D) The proportion of inconclusive test results is equal for all laboratory tests used to detect
pironoma.
- weakens the conclusion
(E) All laboratory tests to detect pironoma have the same proportion of false negative results
- This about this more carefully , if say all laboratory tests have the same proportion of false negative tests , then why would physicians use use any particular one of them.
On the other hand , one test that has the lowest proportion of false positive test is more useful in determining the disease.

Hope this explanation helps !!!!
Kudos me if you like this !!!!!

In tests for pironoma, a serious disease, a false positive result indicates that people have pironoma when, in fact, they do not; a false negative result indicates that people do not have pironoma when, in fact, they do. To detect pironoma most accurately, physicians should use the laboratory test that has the lowest proportion of false positive results.

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

(A) The accepted treatment for pironoma does not have damaging side effects.
(B) The laboratory test that has the lowest proportion of false positive results causes the same minor side effects as do the other laboratory tests used to detect pironoma.
(C) In treating pironoma patients, it is essential to begin treatment as early as possible, since even a week of delay can result in loss of life.
(D) The proportion of inconclusive test results is equal for all laboratory tests used to detect pironoma.
(E) All laboratory tests to detect pironoma have the same proportion of false negative results.

This was a very tricky question indeed. It was like if not 'p', then (1-p) is the answer.

If false negative results are the same for all the laboratories, then false positive results that can be rectified, needs to be chosen.

Thanks.!

Two types of test RESULTS OBTAINED FROM VARIOUS LAB. TESTS are being talked about-
1.False Positive - ( WRONG POSITIVE RESULT) indicates that people have pironoma when, in fact, they do not
2.False Negative- ( WRONG NEGATIVE RESULT) indicates that people do not have pironoma when, in fact, they do

Conclusion-To detect pironoma most accurately, physicians should use the laboratory test that has the lowest proportion of false positive results.

Pre-think-
In order to detect a disease we need- MORE PERCENTAGE OF ACCURATE TRUE RESULTS i.e True positive results and true negative results. And we would also want that the percentage of FALSE RESULTS is low.
The author concludes that physicians should use the laboratory test that has the lowest proportion of false positive results.
But what about false negative results? If the percentage of false negative results is high-will it make the conclusion valid? No.
What if the percentage of false negative results is low- will it make the conclusion valid? Yes.
So the author ASSUMES that false negative results have already been taken into account and are not so relevant to the discussion because all tests may have the same percentage of false negative results or in other words THE TESTS CAN NOT BE DIFFERENTIATED BASED ON THE PERCENTAGE OF FALSE NEGATIVE RESULTS for some reason.

(A) The accepted treatment for pironoma does not have damaging side effects.- Irrelevant .

(B) The laboratory test that has the lowest proportion of false positive results causes the same
minor side effects as do the other laboratory tests used to detect pironoma-Not relevant to the discussion.

(C) In treating pironoma patients, it is essential to begin treatment as early as possible, since
even a week of delay can result in loss of life.- No relevant.

(D) The proportion of inconclusive test results is equal for all laboratory tests used to detect
pironoma.- Weakener because it says that the proportion of false negative results and false positive results is same for all the lab. tests and hence there is no way we can even chose a better test method .

(E) All laboratory tests to detect pironoma have the same proportion of false negative results-
This option is based on pre-thinking approach cited above.
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Hi,

We have to strengthen the argument that to detect pironoma most accurately, physicians should use the laboratory test.

Requirements for most accurately test:
1) least proportion of false results, including both the positive and negative results.
2) argument already mentioned that laboratory test has least false positive results.

Looking for an option: which shows that false negative results for laboratory are lower , or at least equal, than the false negative results for tests other than laboratory.

Option E: This option is what we are looking for. This option shows laboratory tests have the same proportion of false negative results and ,according to argument, it has the lowest proportion of false positive results, thus supporting the argument. Hence, correct answer

Option A: This is good reason for opting the accepted treatment. But the argument is not arguing that we have to move to laboratory tests because of the side effects. The main argument is that we have to move to laboratory tests to detect accurately not on the basis of side effects. Hence, incorrect.

Option B: Again this is good reason for opting laboratory test but on the basis of side effects. Saying laboratory tests have not only lowest proportion of false positive results but also lowest side effects is not strengthen the argument that arguing for ( choose it for least false results i.e detect accurately). There is no knowledge on negative results. Hence, incorrect.

Option C: This is clearly out of scope. Hence, incorrect.

Option D: This is indeed weakening the argument. If the proportion of inconclusive test results is equal for all laboratory tests used to detect pironoma , means this test has more false negative results as , according to the argument , it has the least false positive results. Hence does not provide reasons to select the laboratory tests according on the basis of accurate detection. Hence, incorrect.

+1 kudos if it helped you

True test results:
Person has pironoma and the test says he does.
Person doesn't have pironoma and the test says he doesn't.

False test results:
Person has pironoma and the test says he doesn't - False negative
Person doesn't have pironoma and the test says he does - False positive

To detect pironoma accurately, obviously false test results should be minimised. Now the arguments says that the test with the lowest proportion of false positives should be used. The question that arises is what about false negatives? What if the test with the lowest proportion of false positives has very high proportion of false negatives. Will that test be most accurate then? Perhaps not.
So how do we support the recommendation that the test with lowest false positives should be used (since it will be the most accurate)?
Option (E) says that all tests have the same proportion of false negatives. This means false negatives are the same for all tests. So this is not a distinguishing factor at all. Then the test that has the lowest proportion of false positives would be the most accurate. Hence, option (E) supports the recommendation.

Some people seem to have had trouble with option (C).

(C) In treating pironoma patients, it is essential to begin treatment as early as possible, since even a week of delay can result in loss of life.
This would support focusing on minimising false negatives. A false negative delays the start of treatment. If treatment needs to begin asap, then we should try to minimise false negatives. It doesn't strengthen our recommendation of minimising false positives.

(A) The accepted treatment for pironoma does not have damaging side effects.( WRONG ANSWER :The argument deals with the detection of the disease and not with its treatment.)

(B) The laboratory test that has the lowest proportion of false positive results causes the same minor side effects as do the other laboratory tests used to detect pironoma.(WRONG ANSWER : The argument is not concerned about the side effects of the tests.)

(C) In treating pironoma patients, it is essential to begin treatment as early as possible, since even a week of delay can result in loss of life.(WRONG ANSWER : The argument is concerned with the detection of the disease and not with its treatment.)

(D) The proportion of inconclusive test results is equal for all laboratory tests used to detect pironoma.( WRONG ANSWER : The argument is not about the proportion of inconclusive results.)

(E) All laboratory tests to detect pironoma have the same proportion of false negative results.(RIGHT ANSWER : When all laboratory tests give the same number of false negative results then the only thing that will differentiate a given test from the others will the number of false positive results it produces.)

I think all the above answers miss the point about why precisely A is incorrect:

A is incorrect because if the treatment has no damaging side effects, that would entail using the test with the highest portion of false positives if the aim is that you want to help the highest number of people and there is no other damage

However, this is not related to the conclusion, which states that the main concern is accuracy!
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agree with the explaination. The conclusion is to focus on false possitive test.

Thanks Marc for your post. To be clear here, are you saying the non-bolded portion of the last sentence IS NOT part of the conclusion? It's a seemingly rhetorical question, but I do think it's a valid one considering that conclusions are usually the last sentence.
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ThatDudeKnows avigutman I chose A because treatment not having damaging effects is a valid reason for choosing lower false positive tests because treatments in case of false negative anyway will not cause damaging effects so it makes sense then that they want to focus on lowering false positive. Why is this wrong and why does this reasoning not apply

The presence or absence of damaging side effects has no bearing on the accuracy of detection.
Separately, Elite097, I believe you might have mixed up the definitions of false positive and false negative.

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