LSAT Explanation PT 45, S1, Q24: In criminal proceedings, defense attorneys occasionally

LSAT Question Stem

Which one of the following is an error in the reasoning above? 

Logical Reasoning Question Type

This is a Flaw question. 

Correct Answer

The correct answer to this question is B. 

LSAT Question Complete Explanation

The question type for this problem is a Flaw in the Reasoning question, which asks us to identify the error in the argument presented in the passage.

To summarize and analyze the argument, let's break down its structure:

1. Premise: Defense attorneys sometimes try to acquit suspects by comparing their DNA to DNA samples from the crime scene.

2. Premise: Every person has unique DNA, but DNA tests sometimes fail to distinguish between different people.

3. Conclusion: It is a mistake to exonerate a suspect just because their DNA does not match the DNA samples from the crime scene.

The "Evaluate" question for this argument would be: "Do DNA tests that fail to distinguish between different people also fail to recognize clear mismatches?"

Now let's discuss each answer choice in detail:

a) This answer choice is incorrect because the argument does not assume that physical evidence is never mistaken. In fact, the argument acknowledges that DNA tests sometimes fail to distinguish between different people, which implies that mistakes can be made with physical evidence.

b) This is the correct answer choice. The flaw in the argument is that it confuses a test that incorrectly identifies DNA samples as coming from the same person (false positives) with a test that incorrectly shows as coming from different persons samples that come from a single person (false negatives). Just because the test sometimes fails to distinguish between different people, it does not necessarily mean that it cannot recognize a clear mismatch.

c) This answer choice is incorrect because the argument does not generalize about the reliability of all methods used to identify those involved in the commission of a crime. The argument specifically discusses the limitations of DNA tests and does not mention other methods.

d) This answer choice is incorrect because there is no indication that the author relies on experimental data that have not been shown to hold under nonexperimental conditions. The argument is based on the premise that DNA tests sometimes fail to distinguish between different people, but it does not specify whether this is due to experimental data or other factors.

e) This answer choice is incorrect because the argument does not address whether physical evidence taken from the crime scene is the only sort of evidence that should be admitted in criminal court proceedings. The argument focuses on the limitations of DNA tests in exonerating suspects and does not discuss other types of evidence.