LSAT 109 | Section 1 | Logical Reasoning: Q17

LR Question 17 Explanation

QUESTION TEXT: Expert witness: Ten times, and in controlled…

QUESTION TYPE: Weaken

CONCLUSION: A single drop of the defendant’s blood stains much less than 9.5 square centimeters of the fabric.

REASONING: The expert witness did ten controlled tests and found that the blood stained between 4.5 and 4.8 square centimeters.

ANALYSIS: This sounds like conclusive evidence. But the witness’ sample size is small: ten is not many attempts. And there are many things that could affect blood staining such as heat, humidity, etc.

Answers B and E are ad hominem attacks. Those are almost never relevant unless we have some further evidence that they are true.

___________

1. This is true, but it doesn’t prove that the evidence was not already strong enough.
2. This doesn’t show that this particular witness fudged his evidence. 
3. CORRECT. This number is twice as much as the value from the previous tests. It calls into question the results and indicates that we need to do more tests. This is true even though 9.3 is also less than 9.5.The main point is that it is twice as much as previous results. All of the results now seem unreliable. 
4. What another person’s blood does is irrelevant. The fact that we are measuring this at all implies that each person’s blood stains differently. 
5. That’s true. But we have no evidence that this particular witness is not an expert.