PREP08一道题讨论，欢迎发表不同看法

chuck15

A study followed a group of teenagers who had never smoked and tracked whether they took up smoking and how their mental health changed. After one year, the incidence of depression among those who had taken up smoking was four times as high as it was among those who had not. Since nicotine in cigarettes changes brain chemistry, perhaps thereby affecting mood, it is likely that smoking contributes to depression in teenagers.

Which of the following, if true, most strengthens the argument?

A   Participants who were depressed at the start of the study were no more likely to be smokers after one year than those who were not depressed.
B   The study did not distinguish between participants who smoked only occasionally and those who were heavy smokers.
C   Few, if any, of the participants in the study were friends or relatives of other participants.
D   Some participants entered and emerged from a period of depression within the year of the study.
E   The researchers did not track use of alcohol by the teenagers.
   答案是A。
想问一下B选项去除了 biased sample的可能性，为什么是错的呢？

   

kluivert

After one year, the incidence of depression among those who had taken up smoking was four times as high as it was among those who had not。

Since nicotine in cigarettes changes brain chemistry, perhaps thereby affecting mood, it is likely that smoking contributes to depression in teenagers.

分析一下。假如吸烟和depression没有关系，而depression也不会导致孩子吸烟...那么depression在（A吸烟B不吸烟）应该是一样的...好比你把两种液体均匀混合起来。。不论你取样多少，他们的比例都是一样的
而本题说不一样，depression在A吸烟中的比例远高于在B不吸烟的..
那我们就会考虑是不是 ： 吸烟导致depression ？ 还是depression导致吸烟？
本题又说是吸烟导致depression,要加强它，那我们就要排除depression导致吸烟的可能性

A   Participants who were depressed at the start of the study were no more likely to be smokers after one year than those who were not depressed.
这才是真正排除了取样..心理有问题的孩子不会比心理没问题的孩子更有可能去吸烟...
这句话的真正含义就是  如果吸烟不导致心理疾病，那么有心理问题的孩子在（A吸烟B不吸烟）中的比例应该是一样的  ... 而结果是吸烟的孩子中有心理问题的比不吸烟的多的多...那说明吸烟就会导致心理问题


B   The study did not distinguish between participants who smoked only occasionally and those who were heavy smokers.

这是削弱 ... 说这个研究没有区分偶然吸烟，和重度吸烟... 那么就无法排除这样的可能：心理疾病导致了吸烟

心理疾病 会导致 轻度吸烟,
or 心理疾病 会导致 重度吸烟
无论是上面两个哪个结果，都会推倒出：吸烟中的有心理问题的孩子（ 比 ）不吸烟的有心理问题的孩子 （多）

那不就说明: 心理问题导致了很多孩子开始吸烟
而和题目结论是相反的，自然是削弱了

chuck15

kluivert 发表于 2018-8-24 06:06
After one year, the incidence of depression among those who had taken up smoking was four times a ...

谢谢！

但是我不认同关于B是削弱的解释，我认为是无关选项。要达成削弱的话是：it is unlikely that smoking contributes to depression in teenagers. 但是“ 心理问题导致了很多孩子开始吸烟 ” 并不说明这一点。所以这是无关的。

kluivert

B 选项直接指出这个研究 忽略了 心理问题导致了很多孩子开始吸烟  ( 和结论完全相反 ) 的可能性 ... 难道不是削弱么

chuck15

kluivert 发表于 2018-8-24 10:43
B 选项直接指出这个研究 忽略了 心理问题导致了很多孩子开始吸烟  ( 和结论完全相反 ) 的可能性 ... 难道不 ...

smoking 导致 depression 的 反面 是:  smoking 不会导致 depression， 而不是 depression 导致 smoking。

sorry I insist my standpoint.

kluivert

我终于明白了
B 存在的问题是
没有区分轻度吸烟，重度吸烟
那有可能是 有mental issue 的都是（大部分）轻度吸烟者 ，而重度吸烟者里的有 mental issue 比较少 。。。 那和结论的 “吸烟引起depression”不上了。 应该是重度吸烟的人有depression多才对 ... 所有会削弱

cycgundam

B的问题在于题目条件的区分是take up smoking和not take up smoking。smoking以后的频率是无关的，所以研究区分不区分频率与研究的主题没有关联。

chuck15

cycgundam 发表于 2018-8-26 03:30
B的问题在于题目条件的区分是take up smoking和not take up smoking。smoking以后的频率是无关的，所以研究 ...

同意！