Kyle: The rate of highway fatalities per 100 million miles driven was

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Kyle: The rate of highway fatalities per 100 million miles driven was  
　　about a third lower last year than ten years ago. The decrease is mainly  
　　attributable to greater use of seat belts and to less drinking of alcohol  
　　by drivers, but last year s sluggish economy also contributed, by curtai-  
　　ling driving.  
　  
Lisa: The economy could not have been a factor, because even if fewer  
　　fatalities occur when fewer miles are driven, the number "per 100 million  
　　miles driven" is
what you were discussing, and that figure would not  
　　fall merely because fewer miles were driven.  
Lisa s objection is based on  
A)  indicating, that a confusion between cause and effect has taken place  
B)  distinguishing between total number of instances and rate of occurrence  
C)  proposing an alternative way of interpreting the data presented  
D) pointing out that statistics can be misleading if selected to prove  
a point  
E) showing that lack of precision has caused a relevant ambiguity  答案是B

不明白，求教

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还是不太明白

Thruth

Hello 谢谢你的回复， fatalities per million miles= 总共死亡人数/ 总行驶的公里数， 丽萨认为即使总行驶的公里数下降， fatalities per million miles 也不会下降，是因为她忽略了 ： 总死亡人数也会下降。 是这个意思吗？
但是我还是不明白答案的描述： distinguishing between total number of instances and rate of occurrence.      total number of instances 是指什么呢》

-- by 会员 棒棒dudu (2011/6/3 19:12:56)

Lisa 没有忽略任何东西，Kyle 也不是忽略，而是概念不清楚。他认为里程总数少了，事故致死比率也就少了。这明显不严谨。


此比率=事故致死/里程总数（一百万mile单位）


所以还要考虑事故致死数量才能得到比率。单纯的里程数减少不能单独作为比例下降的原因。


B答案的意思是
区分事件发生比率和样本总量（此处样本总量既可以单独指里程数，也可以指事故致死数）

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棒棒dudu

Hello 谢谢你的回复， fatalities per million miles= 总共死亡人数/ 总行驶的公里数， 丽萨认为即使总行驶的公里数下降， fatalities per million miles 也不会下降，是因为她忽略了 ： 总死亡人数也会下降。 是这个意思吗？
但是我还是不明白答案的描述： distinguishing between total number of instances and rate of occurrence.      total number of instances 是指什么呢》

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UP

hldada

kyle 认为，驾驶员每行驶100 million miles 的车祸死亡率较以前降低了，其中一个原因包括经济疲软，因为经济的不景气，人们开车的次数减少了（也就是说行驶的里程减少了）。
Lisa认为死亡率降低与经济无关，就算是一段时间内能行驶到100 million miles的驾驶员人数降低了，跟他们的车祸死亡率没有关系
B Lisa清楚的把事件发生次数（行驶到100 million miles ）和 发生率（车祸死亡率）分开了
不知道这么说对不对

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