看快思慢想時，作者舉了一個例子如下：
For example,if you believe that 3% of graduate students are enrolled in
computer science (the base rate),and you also believe that the description
of Tom W is 4 times more likely for a graduate student in that field than
in other fields, then Bayes’s rule says you must believe that the
probability that Tom W is a computer scientist is now 11%.
If the base rate had been 80%, the new degree of belief would be 94.1%.
作者提示可用貝氏定理解釋
從這網址找到的解答是
http://goo.gl/jZufs
Convert new base rate to odds:
.03/(1-.03) = .031
Multiply by likelihood to get posterior odds:
4 x .031 = 12.4
Convert back to probability:
12.4/112.4 = .11
但若用我的想法卻是資訊不足
P(A) => 畢業於電腦科目的學生機率
P(B) => 擁有 Tom 個性的人的機率
P(A|B)=P(B|A)*P(A)/P(B)
P(A) ： 3% => 3% of graduate students are enrolled in computer science
P(A|B) ： 80% => the description of Tom W is 4 times more likely for a graduate student in that field than in other fields
但文中卻無提到 P(B) ，所以我認為無法計算
請問這樣的想法是否有錯誤？
若有錯的話，可否幫忙解釋一下解答的算法，感謝
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※ 編輯: zps 來自: 1.174.153.71 (06/22 14:48)