Quantitative Method QA2-4

2008-06-25 8:21 am
Market Researchers, Inc. has been hired to perform a study to determine if the market for a new product will be good or poor. In similar studies performed in the past, whenever the market actually was good, the market research study indicated that it would be good 85% of the time. On the other hand, whenever the market actually was poor, the market study incorrectly predicted it would be good 20% of the time. Before the study is performed, it is believed there is a 70% chance the market will be good. When Market Researchers, Inc. performs the study for this product, the results predict the market will be good. Given the results of this study, what is the probability that the market actually will be good?

回答 (2)

2008-06-25 9:32 am
✔ 最佳答案
Let
G:the market is good
g:the market research is good
P:the market is poor
p:the market research is poor

P(g|G)=0.85
P(p|P)=0.8
p(p|G)=0.15
p(g|P)=0.2

P(G)=0.7,P(P)=0.3
p(g)=p(g|G)p(G)+p(g|P)p(P)=0.655

Want P(G|g)

Since
P(G|g)
=p(g|G)p(G)/p(g)
=0.85*0.7/0.655
=0.9084
2008-06-25 10:27 pm
conditional probability.... not Quantitative Method....

2008-06-25 14:44:23 補充:
myisland8132 has given a very elegant solution with mathematical language,
below is a graphical illustration. http://www.sendspace.com/file/vuxftb


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