PrepTest 113, Section 4, Question 17
A year ago the government reduced the highway(29 more words not shown)
The argument is most vulnerable(9 more words not shown)
- Ahighway traffic has(6 more words not shown)
- Bthe majority of(6 more words not shown)
- Cthere is a(10 more words not shown)
- Dthe new speed(8 more words not shown)
- Ethe number of(15 more words not shown)
Reading the argument
What else changed that year? The lower speed limit might explain the fewer deaths, but perhaps hospitals became easier to reach from the highway. Perhaps police presence increased or a driver-education program improved safety. The timing alone doesn't tell us which explanation is right.
The conclusion is modest: reducing a speed limit can reduce fatalities. That sounds plausible. Still, this particular before-and-after comparison doesn't establish that the new limit produced the improvement. We need to distinguish a change that happened before the decline from a change that helped cause it.
What we’re looking for
The question asks what the argument takes for granted. I'm expecting an assumption that lets the author credit the speed limit instead of some other explanation of the lower death count.
Working the answers
- A
Traffic could have increased while the lower speed limit reduced fatalities. In fact, fewer deaths despite more traffic would make the improvement look even more striking. The author doesn't have to assume traffic failed to increase in order to claim that the lower limit helped.
- B
Why must most drivers obey it? A change in the behavior of a smaller group could still prevent some fatal crashes. The conclusion doesn't say the policy affected every driver, or even most drivers. It says reducing the limit can reduce fatalities. B adds a majority requirement that this claim doesn't need.
- C
Fewer accidents and fewer deaths aren't the same thing. Suppose the number of crashes stayed unchanged but the crashes became less deadly. Fatalities could then fall without a drop in accident frequency. So even if driving speed is relevant to the argument, a relationship between speed and the number of accidents isn't the particular relationship the conclusion requires.
- D
Extra enforcement could help explain an improvement, but the argument doesn't require it. Drivers might respond to the lower posted limit with the same level of enforcement as before. The author could then credit the lower limit without assuming it was enforced more strictly than the old one.
- ECorrect
This gives us an alternative explanation I hadn't predicted: perhaps the previous year was unusually bad. The argument treats it as a fair baseline, but we haven't been given the longer history.
Imagine annual fatalities of 100, 100, 100, 200 and then 100. Those are hypothetical numbers. If the limit changed between the fourth and fifth years, the author could report a dramatic decline from 200 to 100. Looking at all five years, though, we would wonder whether the final year simply returned to the usual level. Comparing only the last two years hides that possibility.
E states the assumption that the earlier year wasn't abnormally high. If it was, that would undermine the author's basis for attributing the decline to the policy. It wouldn't prove the policy had no effect; it would give us another reason the before-and-after figures could look the way they do.
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