Logical reasoning PrepTest 136 · Section 4 · Question 25

Incorrect. If this answer tied the increase in fiber consumption to no change (or an increase) in colon cancer rates, then it may be correct. But by failing to discuss the effect from the stimulus, this answer fails to describe an error in reasoning present.

Incorrect. The argument is specifically about colon cancer, so this is out of scope. And, if anything, this answer would strengthen the argument, whereas we need a possibility that weakens it.

Incorrect. Difficulty of inclusion would only be relevant in an argument that concluded that preventing colon cancer cases is easy, not that eating fiber is a causal factor in that prevention.

Incorrect. This answer aligns with the argument, so it doesn't highlight a possibility the argument overlooks.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Studies: The consumption of a lot of fiber is correlated with low rates of colon cancer, and not a lot of fiber with high rates of colon cancer.
Conclusion: Fiber prevents colon cancer, and a lack of it causes colon cancer.

Answer Anticipation:
Whenever an LSAT argument relies on studies, there are two primary flaws suggested—sampling, and correlation/causation.

Here, the studies are varied and cover people from many countries, so there's no indication of a sampling flaw.

However, all of the studies highlight correlations between different levels of fiber consumption and colon cancer rates, and it concludes from this that fiber consumption is a causal factor in colon cancer (albeit in an inverted relationship—a lack of fiber causes colon cancer). That's a jump from correlation to causation, and so we should expect an answer dealing with it.

However, the question stem asks us to find an answer highlighting a possibility that the argument overlooks, so the answer most likely won't be a normal, abstract description of that flaw. The correlation/causation jump is flawed for generally one of three reasons—it ignores other causes; it ignores the possibility that the cause and effect are reversed; it ignores the possibility that the correlation is a coincidence. The third is rarely used on the LSAT, and the second doesn't make sense here, so we're left with the first. Let's find an answer that says it ignores the possibility that a separate cause is at play here.

Answer Explanation:
This answer brings up another potential cause. If food high in fiber also contains cancer-fighting substances, then it's likely that these substances are responsible for the low colon cancer rates and not the fiber. In bringing in another potential cause that's correlated with fiber, this answer highlights a possibility that the argument itself doesn't consider and rule out.

Key Takeaway:
Whenever an LSAT argument relies on studies, check for a sampling flaw and a correlation/causation flaw. You'll find one of the two a good 8-9 times out of 10!