LSAT Explanation PT 33, S1, Q17: Expert witness: Ten times, and in

LSAT Question Stem

Which one of the following, if true, most undermines the value of the evidence for the expert witness's conclusion? 

Logical Reasoning Question Type

This is a Weaken question. 

Correct Answer

The correct answer to this question is C. 

LSAT Question Complete Explanation

In this passage, the expert witness presents an argument based on a series of tests. They claim that, after ten controlled tests, a single drop of the defendant's blood consistently stains much less than 9.5 cm2 of the fabric. The structure of this argument can be broken down as follows:

Premise: Ten times, a single drop of the defendant's blood was allowed to fall onto the fabric, and the stained area was always between 4.5 and 4.8 cm2.

Conclusion: A single drop of the defendant's blood stains much less than 9.5 cm2 of the fabric.

The question type is Weaken, and we are asked to identify the answer choice that most undermines the value of the evidence for the expert witness's conclusion.

To better understand this argument, let's use a simple example. Imagine a basketball player who shoots free throws. In ten tries, they consistently make 4 out of 5 free throws. Based on this, we conclude that the player's free throw success rate is 80%. An "Evaluate" question for this argument could be, "Is the player's performance consistent across all free throw attempts?"

Now let's examine the answer choices:

a) This answer choice suggests that if there were more test drops, the evidence would be stronger. However, this does not weaken the existing evidence or the conclusion. It merely implies that more data would provide more support.

b) The fact that some expert witnesses have been known to fudge their data does not directly undermine the evidence presented in this specific case. There is no indication that this particular expert witness has manipulated the data.

c) Correct answer. This answer choice reveals that in an eleventh test drop, the stained area was 9.3 cm2, which is much closer to the expected 9.5 cm2. This new data point calls into question the reliability of the previous ten tests and weakens the conclusion that the defendant's blood stains much less than 9.5 cm2 of the fabric.

d) The results from another person's blood are not relevant to the conclusion about the defendant's blood. This answer choice does not undermine the evidence or the conclusion.

e) This answer choice attacks the credibility of expert witnesses in general, but it does not specifically undermine the evidence or the conclusion in this case.

In summary, the correct answer is C because it introduces a new data point that weakens the conclusion that the defendant's blood stains much less than 9.5 cm2 of the fabric. The other answer choices either do not directly address the evidence or the conclusion, or they focus on unrelated factors.