Logical Reasoning

PT107 · S3 · Q8 Each of the following, if true

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The local agricultural official gave the fruit growers of the District 10 Farmers’ Cooperative a new pesticide that they applied for a period of three years to their pear orchards in place of the pesticide they had formerly applied.

Conclusion (concluded that)

The new pesticide is more effective than the old pesticide, at least in the short term, in limiting the loss of certain fruit to insects.

Evidence

During the three years that the new pesticide was applied to pear orchards (in place of the old pesticide), the proportion of pears lost to insects was significantly less than during the previous three years.

Evaluate

This has a classic Explain Curious Fact feel. We have an asymmetric comparison in the evidence, and the author's conclusion is assuming a causal explanation for it.

Curious Fact ... how come the proportion of pears lost to insects was much lower during the 3 years of using the New pesticide than during the previous 3 years of using the Old pesticide?

Author Explanation ... the new pesticide is better, at least in the short term, at limiting the loss of certain fruit to insects.

Goal

We can weaken an Explain Curious Fact argument two ways: 1. suggest an alternate explanation for the curious fact 2. attack the plausibility of the author's explanation

So let's look for four answers that either or .

8.

Each of the following, if true, weakens the official's argument EXCEPT:

  1. Correct

    The amount of fruit that

    Why this is right

    This has no effect on the argument. We're measuring the effectiveness of these pesticides in terms of proportion lost to insects, not number. So it makes no difference if the raw number of pears is getting higher or lower. We're looking at data that says, "during the previous 3 years of using the old pesticide, we lost 13% of our pears to insects. During the 3 years of the new pesticide, we only lost 8% of our pears."

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

    65% picked this

  2. During the past five years,

    Weakens: alternative explanation

    This offers a different explanation for why a lower proportion of pears have been lost to insects recently: it's not because of the new pesticide, it's because of the insect-abatement programs that have been successful. We might worry that the timelines don't match perfectly. We want to explain why the last three years have been better than the previous three years. This talks about something that transcends both three year period. However, it has been gradually implemented over five years. Thus, we'd expect there to be less effect from it 5 years ago, slightly more 4 years ago, and then increasingly more effect during these past 3 years. The timelines don't have to match perfectly. If we think this program has affected the last 3 years more than it's affected the prior 3 years, then it can explain why the last 3 years look better than the prior 3 years.

    9% picked this

  3. Over the past five years,

    Weakens: alternative explanation

    This offers a different explanation for why a lower proportion of pears have been lost to insects recently: it's not because the new pesticide is doing a better job killing insects; it's because there are more birds in our area who prey on these insects. Just like (B), the timelines don't match perfectly, but again this is a change that has gradually shifted over the past five years. Thus, we'd expect there to be more effect in the past 3 years than in the 3 years prior to that.

    6% picked this

  4. Some of the species of

    Weakens: alternative explanation

    This offers a different explanation for why a lower proportion of pears have been lost to insects recently: it's not because the new pesticide is better at killing insects, it's because some of the insects haven't been able to breed (they breed in water and over the past three years the wet habitats have rapidly shrunk). Not as much wetlands, not as many water breeding insects being born, not as many insects to eat our pears.

    6% picked this

  5. The effects of certain pesticides,

    Weakens: plausibility of explanation

    This doesn't quite offer a different explanation for why a lower proportion of pears have been lost to insects recently. But it makes it implausible to think that the change is because the new pesticide is better than the old one. After all, according to this answer, the old pesticide's effects are still felt during this previous 3 year stretch. We can't start measuring the effectiveness of the new pesticide until the old one's effects have worn off, and the old pesticide's effects are still going strong during the last few years (we stopped using it 3 years ago, but the effects persist for several years after it stops being applied).

    13% picked this

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