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数字与比例不等价是指根据一个比例所得出的结论是没有参考意义的。例如，某地居民使用电视观看节目的比例上升了5%，但实际情况是该地总人口数大幅减少才导致了比例上升，在这种情况下，5%的增长具有实际意义吗？答案显然是否定的。这就是数字与比例不等价的情况。鉴于这一可能性，在没有给出基数的时候，不应简单地用百分比来说明问题。
具体结合例题如下（Day 13）：
In an attempt to improve highway safety, Prunty County last year lowered its speed limit from 55 to 45 miles per hour on all county highways. But this effort has failed: the number of accidents has not decreased, and, based on reports by the highway patrol, many drivers are exceeding the speed limit. Prunty County should instead undertake the same kind of road improvement project that Butler County completed five years ago: increasing lane widths,resurfacing rough highways, and improving visibility at dangerous intersections. Today, major Butler County roads still have a 55 mph speed limit, yet there were 25 percent fewer reported accidents in Butler County this past year than there were five years ago.
数字与百分比能够直接等价吗？在没有绝对事故数的前提下，Bulter县的事故率下降了25%能说明问题吗？如果交通流量减少了，那25%的事故下降率有实际意义吗？