黄皮书P491页第81题
A recent report determined that although, only 3 percent of drivers on Maryland highways equipped their vehicles with radar detectors, 33 percent of all vehicles ticketed for exceeding the speed limit were equipped with them. Clearly, drivers who equip their vehicles with radar detectors are more likely to exceed the speed limit regularly than are drivers who do not.
The conclusion drawn above depends on which of the following assumptions?
A: Drivers who equip their vehicles with radar detectors are less likely to be ticketed for exceeding the speed limit than are drivers who do not.
B: Drivers who are ticketed for exceeding the speed limit are more likely to exceed the speed limit regularly than are drivers who are not ticketed.
C: The number of vehicles that were ticketed for exceeding the speed limit was greater than the number of vehicles that were equipped with radar detectors.
D: Many of the vehicles that were ticketed for exceeding the speed limit were ticketed more than once in the time period covered by the report.
E: Drivers on Maryland highways exceeded the speed limit more often than did drivers on other state highways not covered in the report.
答案说选B：Only if the drivers ticketed in this instance are assumed to make a regular habit of exceeding the speed limit can the conclusion be drawn that drivers with radar detectors are more likely to do so regularly than drivers who are not ticketed.可是为什么呢？我想不明白，希望哪个好心人给我解释一下，谢谢！
B的意思是说超速频率和被罚次数是成正比的。
如果这个前提不成立，那就说明可能那些不装雷达的人也经常超速，只不过没有被抓到而已。
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