LSAT 152 | Section 4 | Logical Reasoning: Q15

LR Question 15 Explanation

QUESTION TEXT: Commentator: The reported epidemic of childhood obesity …

QUESTION TYPE: Flawed Parallel Reasoning

CONCLUSION: There’s no childhood epidemic of obesity.

REASONING: Average weight increased only slightly, so obesity rates can’t have risen much.

ANALYSIS: This is a statistical flaw. Average weight and obesity are measuring different things. The average just tells you the middle point of all children’s weights, while obesity depends on how many children are above a certain high-weight threshold.

You can’t assume that because the middle hasn’t moved much, the number of children at the high end hasn’t changed.

Some children could have become significantly heavier while others became lighter, keeping the overall average relatively stable. So the changes cancel each other out when calculating the average, even though the number of obese children has increased.

The flaw is assuming that a stable average means no significant change at the extremes.

___________

1. This uses belief to infer temperature — different flaw.
2. CORRECT. Same structure: small change in average salary → conclude little change in high earners. That’s the same mistake.
3. This is about conversions, we’re talking about averages.
4. This is making a causal argument. We don’t know anything about what might have caused obesity.
5. This is a good argument.