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Chapter 3: Bayesian Networks > 3.5 How Do We Obtain the Probabilities?

3.5 How Do We Obtain the Probabilities?

So far we have simply shown the conditional probability distributions in the Bayesian networks we have presented. We have not been concerned with how we obtained them. For example, in the credit card fraud example we simply stated that P(Age = less30) = .25. However, how did we obtain this and other probabilities? As mentioned at the beginning of this chapter, they can either be obtained from the subjective judgements of an expert in the area, or they can be learned from data. In Chapter 4 we discuss techniques for learning them from data, while in Parts II and III we show examples of obtaining them from experts and of learning them from data. Here, we show two techniques for simplifying the process of ascertaining them. The first technique concerns the case where a node has multiple parents, while the second technique concerns nodes that represent continuous random variables.


  

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