Logical Reasoning

PT110 · S3 · Q21 Thirty years ago, the percentage

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Thirty years ago, the percentage of their income that single persons spent on food was twice what it is today.

Conclusion

Incomes have risen at a greater rate than the price of food in that period.

Evidence

Thirty years ago, single people spent twice as big a percentage of their income on food as they do nowadays.

Evaluate

Whenever we see an author interpret the meaning behind a statistical change, we want to think about other possible ways to interpret that statistic.

Curious Fact ... why do single people spend 1/2 as big a percent of their income on food nowadays, compared to 30 years ago?

Author's Explanation .... food is cheaper (in a relative sense). Incomes have risen faster than food prices.

What could be an alternate way to explain this? Let's say that food prices and incomes have both gone up by 20% since 1990. How could it be that single people nowadays are spending a smaller slice of their income on food?

Maybe they're just eating out less. Maybe they're cooking for themselves more. Maybe they're better at using coupons. Maybe they're just eating less food overall.

Goal

Since we're trying to strengthen the argument, we want to either rule out a different explanation for why single people nowadays spent a lower % of their income on food, or increase the plausibility that incomes have risen faster than food prices.

21.

Which one of the following, if assumed, helps most to justify the conclusion drawn above?

  1. The amount of food eaten

    Less Impactful than Correct Answer

    This helps to rule out the idea that single persons nowadays are spending a lower % of their income on food by simply eating less food. But since this is about all people, not specifically about single persons, it's not as tightly drawn as it could be, and the alternative explanation it's ruling out (maybe they just eat 1/2 as much as before?) is not a compelling one to begin with. So it loses out to the correct answer, in terms of impact.

    14% picked this

  2. In general, single persons today

    Partially Weakens

    To the extent that single people nowadays eat less, this offers an alternate explanation for why they spend a smaller % of their income on food, which weakens the argument. We don't know whether healthier foods is a change that would result in spending a higher / lower % of income on food, so that part as Unclear Impact.

    2% picked this

  3. Correct

    Single persons today, on average,

    Why this is right

    This not only accomplishes what (A) does (it rules out the alternate explanation of "maybe single people just eat less" and accomplishes it even better because it's specifically about single persons), but it also rules out the alternate explanation that single people are spending a lower % on food because they've actually changed their eating habits. So this rules out two alternate explanations for why single people today spent a lower % of their income, and since it establishes that they are basically buying the same food in the same quantity, it's really hard to escape the author's conclusion. If you're buying the same amount of the same stuff, and now that purchase represents a smaller % of your income, then relative size of that purchase compared to your income has shifted in a way that widens the gap between income and food prices.

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

    79% picked this

  4. The prices of nonfood items

    Less Impactful than Correct Answer

    This strengthens somewhat, in the sense that it makes it sound like food prices have been less subject to inflation than have nonfood prices. But it doesn't have nearly the strengthening power of the correct answer, which tells us "there's no difference in what they're buying or how much they're buying". The correct answer nearly guarantees the conclusion, whereas this answer just suggests a whiff of more plausibility to the conclusion.

    4% picked this

  5. Unlike single persons, families today

    Weakens, if anything

    If incomes had risen faster than food prices, then families would also be spending a lower % of their income on food (all other things being equal). So since this answer is telling us that families have not seen a lowering % of income spent on food, it makes the author's conclusion less plausible.

    2% picked this

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