Hey Guys
I can't grasp the reasoning behind the following question.
Appendicitis (inflammation of the appendix) is potentially fatal; consequently, patients with symptoms strongly suggesting appendicitis almost always have their appendix removed. The appropriate surgery is low-risk but performed unnecessarily in about 20% of all cases. A newly developed internal scan for appendicitis is highly accurate, producing two misdiagnoses for every 98 correct diagnoses. Clearly, using this test, doctors can largely avoid unnecessary removals of the appendix without, however, performing any fewer necessary one than before, since...
- the patients who are correctly diagnosed with this test as not having appendicitis invariably have medical conditions that are much less serious than appendicitis.
- the misdiagnoses produced by this test are always instances of attributing to someone who does not, in fact, have it
- all of the patients who are diagnosed with this test as having appendicitis do, in fact, have appendicitis
- every patient who is diagnosed with this test as having appendicitis has more than one of the symptoms generally associated with appendicitis
- the only patients who are diagnosed using this test are patients who lack one or more of the symptoms that are generally associated with appendicitis
Can anybody see the hidden clues?
Cheers
Lukas
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lukaswelker
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ceilidh.erickson
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In this problem, the "since" indicates that we're looking for an EXPLANATION that would keep the given conditions true. The conditions we need to keep true are:
1. Doctors can largely avoid unnecessary removals of the appendix. This doesn't mean avoiding all unnecessary removals - just most of them.
2. Without performing any fewer necessary one than before. This means that every single necessary surgery must be performed - doctors can't miss a single one.
When going through the answer choices, we can eliminate any that suggest that doctors would overlook necessary surgeries.
A. the patients who are correctly diagnosed with this test as not having appendicitis invariably have medical conditions that are much less serious than appendicitis.
Conditions other than appendicitis are not relevant.
B. the misdiagnoses produced by this test are always instances of attributing to someone who does not, in fact, have it
This would tell us that we sometimes have false positives, and might occasionally perform unnecessary surgery. But if none of the diagnoses are false negatives, then everyone who has it will be diagnosed with it -> every necessary surgery will be performed. Correct.
C. all of the patients who are diagnosed with this test as having appendicitis do, in fact, have appendicitis
This leaves open the possibility that some of the people NOT diagnosed might also have appendicitis, and thus some of the necessary surgeries might NOT be performed.
D. every patient who is diagnosed with this test as having appendicitis has more than one of the symptoms generally associated with appendicitis
Symptoms are irrelevant. We just need to know if we've caught every real case, and not flagged most of the non-cases.
E. The only patients who are diagnosed using this test are patients who lack one or more of the symptoms that are generally associated with appendicitis
Again, symptoms are irrelevant.
The answer is B.
1. Doctors can largely avoid unnecessary removals of the appendix. This doesn't mean avoiding all unnecessary removals - just most of them.
2. Without performing any fewer necessary one than before. This means that every single necessary surgery must be performed - doctors can't miss a single one.
When going through the answer choices, we can eliminate any that suggest that doctors would overlook necessary surgeries.
A. the patients who are correctly diagnosed with this test as not having appendicitis invariably have medical conditions that are much less serious than appendicitis.
Conditions other than appendicitis are not relevant.
B. the misdiagnoses produced by this test are always instances of attributing to someone who does not, in fact, have it
This would tell us that we sometimes have false positives, and might occasionally perform unnecessary surgery. But if none of the diagnoses are false negatives, then everyone who has it will be diagnosed with it -> every necessary surgery will be performed. Correct.
C. all of the patients who are diagnosed with this test as having appendicitis do, in fact, have appendicitis
This leaves open the possibility that some of the people NOT diagnosed might also have appendicitis, and thus some of the necessary surgeries might NOT be performed.
D. every patient who is diagnosed with this test as having appendicitis has more than one of the symptoms generally associated with appendicitis
Symptoms are irrelevant. We just need to know if we've caught every real case, and not flagged most of the non-cases.
E. The only patients who are diagnosed using this test are patients who lack one or more of the symptoms that are generally associated with appendicitis
Again, symptoms are irrelevant.
The answer is B.
Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education
EdM in Mind, Brain, and Education
Harvard Graduate School of Education
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ceilidh.erickson
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For more on EXPLAIN A DISCREPANCY, see:
https://www.beatthegmat.com/cr-t155437.html#548469
https://www.beatthegmat.com/centralia-s- ... tml#544276
https://www.beatthegmat.com/building-wit ... tml#539361
https://www.beatthegmat.com/cr-t155437.html#548469
https://www.beatthegmat.com/centralia-s- ... tml#544276
https://www.beatthegmat.com/building-wit ... tml#539361
Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education
EdM in Mind, Brain, and Education
Harvard Graduate School of Education
