Researchers took a group of teenagers who had never smoked and for one year tracked whether they took up smoking and how their mental health changed. Those who began smoking within a month of the study's start were four times as likely to be depressed at the study's end than those who did not begin smoking. 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?
Participants who were depressed at the study's start were no more likely to be smokers at the study's end than those who were not depressed.
Participants who began smoking within a month of the study's start were no more likely than those who began midway through to have quit smoking by the study's end.
Few, if any, of the participants in the study were friends or relatives of other participants.
Some participants entered and emerged from a period of depression within the year of the study.
The researchers did not track use of alcohol by the teenagers.
避免因果倒置!
两种现象同时出现,加强一种因果关系,排除因果倒置。
a的意思是说,已经抑郁的人不会更有倾向去吸烟。这个从反面证明了吸烟导致抑郁。因为如果抑郁的人会更倾向去喜欢去吸烟,那么测试结果就可能因为样本bias而出现偏差:即抑郁的人喜欢吸烟,所以吸烟人群中抑郁的人多。而排除了这种可能性使得实验更加valid。确实绕。
相关因果
depress + & smoker+ ➡️ smoking导致depress
说明不是果导致了因
前提:Since nicotine in cigarettes changes brain chemistry, perhaps thereby affecting mood, it is likely that smoking contributes to depression in teenagers.
结论:Those who began smoking within a month of the study's start were four times as likely to be depressed at the study's end than those who did not begin smoking.
加强的一种方式:排除他因
关于b选项和a选项有一点突发奇想。b选项其实也是在增强“先抽烟的更难戒烟“,那么在一定条件下肯定是能够增强逻辑链条的,如果它是一个目标推理题或者导致结果问你assumption的题,那么b也是对的。这里不选是因为这是一道体现影响力(explanation)的题,他不能体现抽烟对抑郁症的影响力,要体现影响力,还是得靠排他因!
A排除了一开始就抑郁这个因素
实验开始的一个月内吸烟的青少年得抑郁症的概率是不吸烟的青少年得抑郁症概率的4倍,又因为尼古丁可以改变大脑化学物质。所以吸烟导致了青少年的抑郁症。问support
choice a, 在实验开始就已经得抑郁症的青少年,并不会比那些不得抑郁症的青少年,在实验结束之前开始吸烟。correct,排除了因果倒置
d选项some这个意思就不对。
A.属于排他因型加强,这里的他因是因果倒置的情况
文中说因为吸烟和抑郁这两件事有关系,所以吸烟导致抑郁
而反驳可以说其实是抑郁导致吸烟,所以它们两才有关系。
而A就是排除了这个反驳的情况,说抑郁的人才不会更容易吸烟呢,其实就是加强了结论。
相关因果,削弱优先考虑 逆向因果
A 在实验开始时就抑郁的人没有比不抑郁的人更可能成为实验结束时的吸烟者
排除抑郁导致吸烟这一可能,加强吸烟导致抑郁
这种 由两者的相关性去推倒因果很容易出现的问题:①第三因(控制变量)②因果关系颠倒
排除他因,排除掉这些抑郁的人是因为已经抑郁了,加强证明这些人抑郁是因为吸烟
目前看到的最难的CR
一开始就抑郁的人不影响吸烟抑郁比率,排除他因
这是一个因果倒置的例子
不是逆命题