Logical ReasoningDifficulty: Easy

PT152 S4 Q15 Explanation

Commentator: The reported epidemic

A free, expert breakdown of this official LSAT Logical Reasoning question.

TopicsParallel Flaw

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Stimulus

Commentator: The reported epidemic of childhood obesity in our country is a myth. Over the last 8 years, there was only a 1 pound (0.45 kilogram) increase in children’s average weight. This is not a substantial who are obese cannot have increased substantially.

What this question is testing

Parallel Flaw

Your task

Break the argument into its conclusion and evidence, then do exactly what the question stem asks with that structure.

Common trap

Answers that sound relevant to the topic but don't connect to the argument's actual reasoning.

Winning move

Predict what a right answer must do, then test each choice against the conclusion-evidence gap.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question
15.

Which one of the following contains flawed reasoning most similar to the flawed reasoning contained in

Answer choices

  1. Bad Premise / Conclusion Match1% picked this

    The average summer temperature over the past five years must have increased, since most people believe that

    Here, the conclusion is about average (average should be the premise), and the premise is about what people believe, when the other half of the argument is supposed to be a claim about proportion / ratio / fraction / percentage of a subset.

  2. Correct90% picked this

    The proportion of employees who earn very high salaries must not have increased more than slightly over the last year, since the average salary

    Why this is right

    The conclusion is about proportion and the evidence is about average. Huzzah! Our same objection would apply here: it's possible that a much higher percentage of people now make very high salaries. If, simultaneously, a lot of people now make much lower salaries, those two effects will balance out and cause the average to increase only slightly.

    Skill tested: Parallel Flaw · how this choice captures the argument's function is the move to repeat next time.

  3. Bad Premise Match4% picked this

    The proportion of apartment buildings in the downtown area must have increased substantially in recent years, since a substantial number of office buildings have

    The conclusion is correctly about proportion, but the premise is supposed to be about average. Instead, it's about number. Also, the original argument was saying "since average barely moved, proportion barely moved". This one is saying "since there's a substantial number of new apartment building, there must be a substantial increase to the proportion".

  4. Reversed Premise / Conclusion2% picked this

    The average weight of adults must have increased in the last few years, since restaurants have increased the proportion of high-calorie dishes

    Here, the conclusion is about average and the support is about proportion. The original argument had those two ingredients reversed.

  5. Reversed Premise / Conclusion4% picked this

    The average price of a house must be increasing, since the proportion of household income spent on housing has increased

    Again, the conclusion is about average and the support is about proportion. The original argument had those two ingredients reversed.

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