In criminal proceedings, defense attorneys occasionally attempt to establish that a suspect was not present at the co...

Mehran on November 8, 2013

The conclusion of the argument is: "...it is a mistake to exonerate a suspect simply because that person's DNA did not match the DNA samples taken from the scene of the crime."

Why? Because "DNA tests often fail to distinguish among DNA samples taken from distinct individuals."

Notice that this argument makes absolutely no sense. Defense attorneys attempting to establish that their client was not present at the commission of a crime by using DNA samples would be comparing the suspect's DNA to the DNA found at the scene of the crime. This, however, would not be failing to distinguish among DNA samples taken from distinct individuals.

In fact, these are two completely different things (i.e. distinguishing among the DNA samples of distinct people and comparing DNA samples from a crime scene to the DNA of a specific person). Therefore, this argument is flawed.

(B) is the the CORRECT answer. The language is vague, but it is describing the jump made between these two tests.

The author's conclusion would make sense if the issue with DNA tests put forth by the author in the passage was that DNA samples from the same person are incorrectly identified as coming from different people. Because then, it would be correct that it would be a mistake to exonerate a suspect simply because that person's DNA did not match the DNA samples taken from the scene of the crime (i.e. DNA samples from the same person are sometimes incorrectly identified as coming from different people).

This, however, is not the issue with DNA tests put forth by the author in the passage. The author states "DNA tests often fail to distinguish among DNA samples taken from distinct individuals (or as stated in answer choice B, "a test that incorrectly shows as coming from different persons samples that come from a single person").

When the wording of an answer choice is especially vague, as it is here, try breaking apart the answer phrase by phrase. Always relate the abstract language back to what is being discussed in the argument. That will better help you see whether or not the answer choice applies.

Also, do not forget the power of process of elimination on Methods of Reasoning/Errors in Reasoning questions because even if you cannot pinpoint exactly what the author is doing, you can definitely tell what he or she isn't doing. For example, in this question, (A), (C), (D) and (E) can easily be eliminated, which would allow you to focus your attention on (B).

Hope this helps! Please let us know if you have any other questions!