PrepTest 143, Section 4, Question 9
In a sample containing 1,000 peanuts from lot(52 more words not shown)
The reasoning in which one(13 more words not shown)
- AEvery one of(23 more words not shown)
- BIf a plant(31 more words not shown)
- CIn the past(42 more words not shown)
- DThree thousand registered(41 more words not shown)
- EAll of my(27 more words not shown)
Reading the argument
The samples are the same size, so the different infection counts are meaningful. Fifty infected peanuts out of 1,000 is 5 percent. Two hundred out of 1,000 is 20 percent. The sample from lot B has the higher infection rate, and the author uses that difference to conclude infection is more widespread in lot B overall.
That is a straightforward comparison from samples to the groups they represent. We aren't explaining why the peanuts became infected, and we aren't following a chain of rules. We compare how common a feature is in two equally sized samples, then carry the comparison over to the larger groups.
What we’re looking for
For a parallel, imagine sampling equal numbers of cows from two herds, finding spots more often in one sample, and concluding spots are more common in that herd. The subject can change completely. What matters is keeping the two groups, comparable samples, and conclusion about which group has more of the feature.
Working the answers
- A
The parts are good, so the assembled machine must be good. That transfers a quality from components to a whole. There aren't two populations with samples showing different rates of a feature, so it doesn't match the comparison between peanut lots.
- B
Careless treatment is linked to blight, and blight is linked to death. The conclusion connects the beginning and end of that chain. The peanut argument doesn't connect successive likely consequences; it compares infection rates in samples from two groups.
- C
This concludes that the fungicide caused the infection to disappear. The observations before and after treatment are being used to identify a cause. Our argument never concludes that being in lot B causes infection; it only concludes that infection is more widespread there. The causal claim, not the mention of plants or the number 1,000, is the decisive difference.
- DCorrect
The two parties correspond to the two peanut lots. The 1,500 surveyed voters from each party correspond to the equal samples of 1,000 peanuts. Favoring Pollack corresponds to being infected: it is the feature whose frequency is being compared.
More sampled Liberals favor Pollack than sampled Conservatives do, just as more sampled lot B peanuts are infected than sampled lot A peanuts. The conclusion carries that sample comparison over to the groups: Pollack has more support among Liberals. The numbers needn't be identical; the reasoning is the same.
- E
My livestock belong to the registered group, and the registered group excludes free-range livestock. The conclusion applies that exclusion to my livestock. This uses membership in one group to apply a rule, rather than comparing samples from two groups to estimate how common a feature is.
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