今天（20th June）更新一下答案
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今天看Financial Econometrics 的一个quiz
You are given the following information:
给你以下信息：
Mary is a quiet, studious and very concerned with social issues, while an undergraduate at Berkeley, she majored in English literature and Environmental studies.
玛丽毕业于加州伯克利，是一个安静，勤学关注社会事务的人。她在大学里主修英语文学和环境研究
given this information, indicate which of the following three cases is most probalbe:
以下三个选项那个的可能性更大？
(A) Mary is a Librarian, 玛丽是个图书管理员
(B) Mary is a librarian and a member of the Sierra Club, 玛丽是个图书管理员，并且是某环境保护组织的成员
(C) Mary works in the Banking industry 玛丽在银行业工作
What is your opinion? and Why?
Sierra Club 是一个环保组织
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1.The best answer is (C). There are so many more people employed by banks than by libraries that it is far more likely someone is a banker than a librarian.
C是最好的答案，因为在银行工作的人要远远超过当图书馆管理员的（想想你认识的人当中有人是图书馆管理员吗？）
2.If you chose (A) your brain is probably making a representativeness mistake. You have assumed that because Mary demonstrates a few traits of librarians (quiet and studious), she is one. In reality it is statistically much more likely that she is a banker.
选A的人就是犯了“代表性”错误，你假设了mary具有图书管理员的特征，但统计上她更可能在银行工作。
3.The worst and most common answer is (B). This is a pure error in probabilities because the joint probability of being both a librarian and a member of the Sierra Club has to be smaller than the simple probability of being a librarian.
最差和最常见的答案是B，这纯粹是个统计学错误。同时是librarian和sierra club member的联合概率当然要小于单纯是libarian的概率。
这些问题是所谓行为金融学研究的，behavior finance, 算是个新兴的流派。在早期金融学的假设里，都是简单的认为市场的参与者是 risk averse 风险厌恶 和 rational behavior理性行为的。但是behavior finance 学派的人主张人的rational action是不同的，对于市场的事件 information，有的人会 overreacting反映过激, 也有人 underreacting反映不足。 于是，如果你能够做出正确的判断，特别是如果能够对市场的反映做出正确的判断，就可以赚到钱了。通俗的说，就是如果你比别人聪明，看的清楚，就能赚钱。
估计索罗斯那种人就是选C的吧？
