PrepTest 125, Section 2, Question 21
Most people who become migraine sufferers as adults(30 more words not shown)
The flawed pattern of reasoning(15 more words not shown)
- AMost good-tempered dogs(21 more words not shown)
- BMost vicious dogs(29 more words not shown)
- CMost well-behaved dogs(19 more words not shown)
- DMost of the(24 more words not shown)
- EMost puppies are(28 more words not shown)
Reading the argument
Imagine arguing that most lawyers went to elementary school, so going to elementary school makes someone likely to become a lawyer.
Of course not. That school history could be extremely common among people who never become lawyers. Knowing what most lawyers did as children doesn't tell us what most children with that history will become.
That's the problem here. We start with adults who suffer migraines and learn that most had bouts of depression as children. Then we switch groups. Now we're looking at a child with that history and predicting migraines in adulthood. But how many such children develop migraines? The passage never tells us. For all it says, that could be only a small fraction.
What we’re looking for
To match the flaw, look for the same switch: most members of one group have a certain history, so someone with that history is probably a member of that group. As we read each answer's first sentence, try predicting the matching conclusion before reading the one it actually gives.
Working the answers
- ACorrect
Most good-tempered dogs were vaccinated as puppies. Good-tempered dogs correspond to adults with migraines; vaccination corresponds to the childhood history of depression. The answer then starts with a vaccinated puppy and predicts a good-tempered dog, just as the original starts with the childhood history and predicts migraines. But vaccination could also be common among dogs that aren't good-tempered. Neither argument tells us how often people or animals with the earlier characteristic develop the later one.
- B
This starts with a vicious dog and looks back toward bad treatment, following the direction of the premise. To match our mistake, it would need to start with a badly treated dog and predict that the dog would become vicious. There could be a separate question about whether this particular owner inflicted the earlier treatment, but that wouldn't be the original's switch between groups.
- C
To match, we'd want: most well-behaved dogs had training, so a trained dog is likely to be well behaved. C instead starts with a dog that didn't have training and rules out good behavior entirely. 'Most' leaves room for well-behaved dogs without training. That's a different error from the original's prediction about someone who has the earlier characteristic.
- D
This introduces a comparison of illness and accident rates. Knowing most veterinary patients are dogs doesn't establish that dogs are more prone to those problems; perhaps there are simply more dogs. To follow our original pattern, the conclusion would instead predict that a dog is likely to be taken to a veterinarian. D draws a different conclusion.
- E
The conclusion stays with a puppy and applies the stated typical timing once that puppy is older than eight weeks. It doesn't start with the group of animals taken from their mothers and infer that a member of that group is probably a puppy. There is no matching switch from the second group back to the first.
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