以下是引用apanapan在2004-3-17 4:33:00的发言：94. When 100 people who have not used cocaine are tested for cocaine use, on average only 5 will test positive. By contrast, of every 100 people who have used cocaine 99 will test positive. Thus, when a randomly chosen group of people is tested for cocaine use, the vast people is tested for cocaine use, the vast majority of those who test positive will be people who have used cocaine.
A reasoning error in the argument is that the argument
(A) attempts to infer a value judgement from purely factual premises
(B) attributes to every member of the population the properties of the average member of the population
(C) fails to take into account what proportion of the population have used cocaine
(D) ignores the fact that some cocaine users do not test positive
(E) advocates testing people for cocaine use when there is no reason to suspect that they have used cocaine
正确答案是C)可是怎么也和题目挂不上钩。私下盼望D)如果是ignores the fact that some people test positive even they never used cocaine 那我就毫不犹豫地选它。可惜不是。这道题该怎么考虑请指教。
这题我刚做过，赫赫。
虽然没用过cocaine的人5%positive,用过的人99%positive.
但是注意，对整个随机人群（含有两类人：用过的和没用过的）进行测试时，应注意这两类人的比例。eg:如果用过的占整人群1%，而没用过的占99%，即使前者positive的人比例为0，后者positive的比例为100%,总体中positive的人也不过是1%。
D选项是个作用不确定选项，因为有一些测试错误，不一定会导致结论不成立。上面这个例子也可以证明这一点。
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发表于 2004-3-17 04:33:00
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