LSAT Explanation PT 27, S1, Q23: Research indicates that 90 percent of

LSAT Question Stem

Which one of the following most accurately describes a flaw in the argument's reasoning? 

Logical Reasoning Question Type

This is a Flaw question. 

Correct Answer

The correct answer to this question is C. 

LSAT Question Complete Explanation

Let's first analyze the argument presented in the passage. The argument's structure is as follows:

Premise 1: Research indicates that 90 percent of extreme insomniacs consume large amounts of coffee.

Premise 2: Tom drinks a lot of coffee.

Conclusion: It is quite likely that Tom is an extreme insomniac.

The question type is a Flaw question, which asks us to identify the flaw in the argument's reasoning.

Before discussing the answer choices, let's consider an "Evaluate" question for this argument: "What is the percentage of people who drink large amounts of coffee and are extreme insomniacs?"

Now, let's discuss each answer choice:

a) It fails to acknowledge the possibility that Tom is among the 10 percent of people who drink large amounts of coffee who are not extreme insomniacs.

- This answer choice is incorrect because the argument does acknowledge this possibility by stating that it is "quite likely" that Tom is an extreme insomniac, rather than definitely.

b) It fails to consider the possible contribution to extreme insomnia of other causes of insomnia besides coffee.

- This answer choice is incorrect because the argument is not concerned with the causes of extreme insomnia, but rather the likelihood of Tom being an extreme insomniac based on his coffee consumption.

c) It relies on evidence that does not indicate the frequency of extreme insomnia among people who drink large amounts of coffee.

- This is the correct answer. The argument tells us that 90% of extreme insomniacs drink large amounts of coffee, but it doesn't provide information on the percentage of heavy coffee drinkers who are extreme insomniacs. Without this information, we cannot accurately determine if Tom is likely to be an extreme insomniac based on his coffee consumption.

d) It draws an inference about one specific individual from evidence that describes only the characteristics of a class of individuals.

- This answer choice is incorrect because the argument is not making a whole-to-part fallacy. The argument is attempting to determine the likelihood of Tom being an extreme insomniac based on a characteristic he shares with a group of individuals (drinking large amounts of coffee).

e) It presumes without warrant that drinking coffee always causes insomnia.

- This answer choice is incorrect because the argument does not claim that drinking coffee causes insomnia. It simply states that there is a correlation between extreme insomniacs and heavy coffee consumption.

In summary, the correct answer is C because the argument relies on evidence that does not indicate the frequency of extreme insomnia among people who drink large amounts of coffee. Without this information, we cannot accurately determine if Tom is likely to be an extreme insomniac based on his coffee consumption.