- PowerScore Staff
- Posts: 8950
- Joined: Feb 02, 2011
- Thu Jan 21, 2016 12:00 am
#36290
Complete Questions Explanation
Flaw in the Reasoning. The correct answer choice is (B)
In this stimulus, the author presents the fact that defense attorneys sometimes try to acquit suspects
by comparing DNA samples from the suspect to DNA samples from the crime scene. But, even
though every person has unique DNA, sometimes the DNA test does not distinguish between
different people. Thus, according to the author, it is a mistake to exonerate a suspect just because the
DNA of the suspect does not match the DNA from the scene.
Most students read the stimulus and think that the reasoning is valid, and so they are surprised when
the question stem asks for the fl aw in the reasoning. When this occurs, you should immediately
glance at the stimulus again to see if you missed an important word or phrase. If you did understand
the stimulus, use the answer choices to get a better sense of what fl aw you might have missed.
The fl aw in the reasoning is discussed in detail in the discussion of the correct answer choice.
Answer choice (A): This choice is wrong, because if the argument assumed that evidence can never
be mistaken, then the argument would not have concluded that DNA evidence can be mistaken.
Additionally, this answer addresses physical evidence, a broader concept than DNA.
Answer choice (B): This is the correct answer choice. This choice can be somewhat confusing
to read, and many students select this answer not so much because they understand exactly what
it means but because they know the other answers are incorrect (and such an approach is perfectly
valid on the LSAT).
In reality, these DNA tests are imperfect because they “sometimes fail to distinguish among samples
taken from distinct individuals.” That is, the test sometimes “incorrectly identifi es DNA samples as
coming from the same person.” So the test sometimes produces false positives. Based on this fact,
the author mistakenly believes the test also produces false negatives; that it cannot reliably rule out
suspects whose DNA doesn’t match crime scene samples.
In other words, this is the fl aw in the reasoning, and the point that the author apparently missed: Just
because the test cannot distinguish every sample of DNA from every other sample, this does not
necessarily mean that it is unable to recognize a clear mismatch.
Answer choice (C): This response is incorrect because the stimulus discusses only DNA evidence
and does not discuss the reliability of “all methods.”
Answer choice (D): There is no indication that the author has relied on data that did not hold up
under non-experimental questions, and this answer choice certainly does not describe the logical fl aw
the author made in moving from the premises to the conclusion.
Answer choice (E): The issue of other evidence aside from DNA evidence is irrelevant because the
author addresses only DNA evidence (and, if anything, the stimulus actually supports the idea that
other evidence is required, not that other evidence should not be admitted).
Flaw in the Reasoning. The correct answer choice is (B)
In this stimulus, the author presents the fact that defense attorneys sometimes try to acquit suspects
by comparing DNA samples from the suspect to DNA samples from the crime scene. But, even
though every person has unique DNA, sometimes the DNA test does not distinguish between
different people. Thus, according to the author, it is a mistake to exonerate a suspect just because the
DNA of the suspect does not match the DNA from the scene.
Most students read the stimulus and think that the reasoning is valid, and so they are surprised when
the question stem asks for the fl aw in the reasoning. When this occurs, you should immediately
glance at the stimulus again to see if you missed an important word or phrase. If you did understand
the stimulus, use the answer choices to get a better sense of what fl aw you might have missed.
The fl aw in the reasoning is discussed in detail in the discussion of the correct answer choice.
Answer choice (A): This choice is wrong, because if the argument assumed that evidence can never
be mistaken, then the argument would not have concluded that DNA evidence can be mistaken.
Additionally, this answer addresses physical evidence, a broader concept than DNA.
Answer choice (B): This is the correct answer choice. This choice can be somewhat confusing
to read, and many students select this answer not so much because they understand exactly what
it means but because they know the other answers are incorrect (and such an approach is perfectly
valid on the LSAT).
In reality, these DNA tests are imperfect because they “sometimes fail to distinguish among samples
taken from distinct individuals.” That is, the test sometimes “incorrectly identifi es DNA samples as
coming from the same person.” So the test sometimes produces false positives. Based on this fact,
the author mistakenly believes the test also produces false negatives; that it cannot reliably rule out
suspects whose DNA doesn’t match crime scene samples.
In other words, this is the fl aw in the reasoning, and the point that the author apparently missed: Just
because the test cannot distinguish every sample of DNA from every other sample, this does not
necessarily mean that it is unable to recognize a clear mismatch.
Answer choice (C): This response is incorrect because the stimulus discusses only DNA evidence
and does not discuss the reliability of “all methods.”
Answer choice (D): There is no indication that the author has relied on data that did not hold up
under non-experimental questions, and this answer choice certainly does not describe the logical fl aw
the author made in moving from the premises to the conclusion.
Answer choice (E): The issue of other evidence aside from DNA evidence is irrelevant because the
author addresses only DNA evidence (and, if anything, the stimulus actually supports the idea that
other evidence is required, not that other evidence should not be admitted).