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Screening test

by GmatKiss » Fri May 25, 2012 12:47 pm
Before lead poisoning starts to cause serious damage, it can be detected through a screening test. Every test sometimes produces false positives, indicating that the people tested have lead poisoning, when, in fact, they do not; a false negative indicates that people do not have lead poisoning when, in fact, they do. To detect lead poisoning most accurately, medical workers should use the screening test which has the lowest proportion of false negative results.

Which of the following, if true, most strongly supports the above recommendation?

The test with the lowest false negative rate also requires the most time-intensive laboratory procedures.

All screening tests used to detect lead poisoning have the same proportion of false positive results.

The proportion of inconclusive test results is equal for all screening tests used to detect lead poisoning.

The screening test which has the lowest proportion of false negative results causes side effects less frequently than other tests.

The treatment for lead poisoning, called chelation therapy, sometimes has serious side effects.
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by Bill@VeritasPrep » Fri May 25, 2012 12:51 pm
The goal is to detect lead poisoning as accurately as possible. How will we accomplish this? By minimizing the number of false negatives.

A--Lab procedures and their time-intensiveness are irrelevant to the goal.

B--Yes. There are two types of inaccurate results: false positives and false negatives. If all tests have the same proportion of false positives, then the only way to differentiate is to look at the proportion of false negatives.

C--This does not affect the recommendation

D--Side effects are not considered in the recommendation, and they are irrelevant to the goal.

E--There is nothing in the recommendation about the treatment; we are only concerned with detecting the poisoning in the first place.
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by GMAT Kolaveri » Tue May 29, 2012 9:13 am
easy one. B
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by Gaurav 2013-fall » Wed May 30, 2012 9:41 am
straight B
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by dhonu121 » Wed May 30, 2012 10:24 am
Yeah B it is.
If the propotion of false-positive is same in all screening test, the better one can be expected to have low false negatives.
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by karthikpandian19 » Thu Jul 12, 2012 9:05 pm
This argument claims that, to ensure the most accurate early detection of lead poisoning, the test with the lowest number of false negatives should be preferred. False negative results erroneously indicate that a person with lead poisoning does not have lead poisoning. Such results prevent patients with lead poisoning from getting treatment. These are clearly undesirable.

We want some statement that further supports the author's conclusion. The correct answer will either indicate an additional benefit of the test with the lowest rate of false negative results or will perhaps describe why other tests are no better.

Choice B tells us all tests have "the same proportion of false positive results." If the test with the lowest number of false negatives is just as good as other tests at avoiding false positives, it is more likely to be the most accurate test overall. This does support the author's conclusion. Choice B is correct.

Choice A: Opposite, irrelevant. The argument does not concern which test requires the "most time-intensive" procedures. If anything, a slower test might delay crucial treatment, which would be bad for patients generally. So, even if this choice were relevant, it would refute, not support the idea that the test with the lowest proportion of false negatives is best.

Choice C: Too weak. This choice says that all available tests produce inconclusive results at the same rate. While producing no more inconclusive results certainly does not refute the author's argument, inconclusive results, when they occur, do not affect the accuracy of the test nearly as much as false results. Thus, this choice is far weaker than Choice B.

Choice D: Irrelevant. This choice says that the test with the lowest proportion of false negatives also "causes side effects less frequently." A lower incidence of side effects is a desirable quality for a test, but it is wholly independent of the accuracy of the test results. This argument is interested only in accuracy.

Choice E: Opposite, irrelevant. If the treatment for lead poisoning can have "serious side effects," then it is undesirable to treat people for lead poisoning unless they actually have lead poisoning. This suggests that we want the test with the lowest false positive rate, so no one who does not have the condition gets the risky treatment. Further, this fact has nothing to do with the accuracy of the test that the author supports.

Choice B is correct.
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