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Summary 163
where the resulting decision tree is asymmetric) is more problematic.
In these instances, the influence diagram approach to decision tree
structuring can be used as a guide only.
From our overview of influence diagrams you will have seen that such
diagrams aid subsequent structuring of decision trees. They allow the
easy insertion of additional acts and events as the decision maker talks
through the decision problem with the decision analyst. (See stages 1
and 2 of Figure 6.9.) By themselves, influence diagrams do not aid in the
creation of decision options or in the recognition of event possibilities. Such
creation and recognition activities perhaps may be best thought of as
creative behavior. As we have seen, Fischhoff et al. found that people
seem to suffer from ‘out of sight, out of mind’ bias when evaluating the
completeness of decision tree-type representations of knowledge.
In other words, individual decision makers may be inappropriately
content with decision problem representations that are created early in
the decision maker/analyst interaction. One major way to combat this
tendency is to subject initial problem representations to outside critique
by other people with a knowledge of the decision problem domain. Such
critiques are readily available in the context of decision conferencing,
where those individuals with a stake in a key decision interact with the
aid of a decision analyst who acts to facilitate a decision. We will deal
with this approach in detail in Chapter 12, where we will focus on the
advantages and disadvantages of group decision making.
Summary
In this chapter we have illustrated the construction of decision trees and
the rollback method for identifying the optimal policy. We described an
approximation method for dealing with continuous probability distributions
within decision trees and summarized some practical applications
of decision trees within decision analysis. Finally, we analyzed the process
of generating decision tree representation of decision problems and
advocated the influence diagram as a key technique to facilitate decision
structuring.
Despite the benefits of using decision trees some decision analysts
counsel against using them too early in the decision process before
a broad perspective of the decision problem has been obtained. For
example, Chapman and Ward 19 argue that decision trees should often
be embedded in a more wide-ranging analysis that includes assessments