PrepTest 129, Section 3, Question 10
Columnist: The failure of bicyclists to obey traffic(49 more words not shown)
The columnist's reasoning is flawed(3 more words not shown)
- Apresumes, without providing(16 more words not shown)
- Bimproperly infers the(11 more words not shown)
- Cfails to consider(13 more words not shown)
- Dfails to provide(7 more words not shown)
- Efails to consider(13 more words not shown)
Reading the argument
Are those two groups of accidents different groups? A cyclist could violate a traffic rule and have inadequate safety equipment in the very same crash.
The columnist gives us two facts: failure to obey regulations is a causal factor in more than a quarter of bicycle accidents, and inadequate equipment is a factor in more than a quarter. Let's accept those facts. The problem appears when the columnist adds the groups to claim that bicyclists are at least partly responsible for more than half the accidents.
Imagine 100 accidents. In 26, disobeying regulations contributes to the crash. In those same 26, inadequate equipment also contributes. Both premises would be true: each factor appears in more than a quarter. But we have identified only 26 accidents, not 52. Counting each factor separately does not turn one accident into two.
What we’re looking for
We might also ask how contributing factors establish responsibility in each case. But even granting that connection, the counting problem remains. For the flaw question, I'd look for the possibility that the factors occur together, leaving fewer distinct accidents than the columnist assumes.
Working the answers
- A
Saying bicyclists are at least partly responsible does not rule out motorists also being a factor. Both could contribute to the same crash. The argument neither gives a percentage for motorists nor needs their involvement to be below half.
- B
The premises already describe these as causal factors. The columnist is not merely observing that two things occur together and then inventing a causal relationship. The disputed move is adding the groups to reach a conclusion about how many accidents involve bicyclists' responsibility.
- CCorrect
More than one factor can contribute to one accident. If violating regulations and inadequate equipment both contribute to the same accidents, adding their separate percentages counts those accidents twice. Our example satisfies both premises with only 26 distinct accidents, so the conclusion of more than half does not follow.
- D
We can grant the figures and still expose the mistake. Even perfectly accurate percentages do not tell us how much the groups overlap. Naming a source for the numbers would not supply the missing information about which accidents occur in both groups.
- E
The conclusion concerns the proportion of accidents for which bicyclists are partly responsible, not the severity of resulting injuries. A scraped knee and a serious injury may differ greatly in harm, but that difference does not solve the problem of counting one accident twice.
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