|The DTREE Procedure|
The order of stages is an important issue in structuring the
decision problem. This sets the sequence of events
or a time horizon and determines when a decision has to be made and when
a chance stage has its uncertainty resolved. If a decision
stage precedes another decision stage in the stages order,
the decision to the right is made after the decision to the
left. Moreover, the choice made in the first decision is
remembered by the decision maker when he or she makes the second
decision. Any chance stages that occur to the left of a
decision stage have their uncertainty resolved before the
decision is made. In the other words, the decision maker
knows what actually happened when he or she makes the decision.
However, the order of two chance stages is fairly arbitrary
if there are no other decision stages between them.
For example, you can change the order of stages `
in the oil wildcatter's problem without affecting the
PROC DTREE determines the order (from left to right) of all
stages specified in the STAGEIN= data set.
The ordering is
based on the rule that if stage
A is the successor of an outcome of
B, then stage
A should occur to the right of (or after)
With the MOVE statement, you can change this order.
The MOVE statement
is very useful in determining the value (benefit or penalty) of
postponing or hurrying a decision.
In particular, the value of perfect information
about an uncertainty can be determined by moving the corresponding
chance stage to the beginning. However, as mentioned in early
sections, the results may be misleading if you use the
MOVE statement without care.
See the "Input Data Sets" section for an example.
Suggestions for preventing this are as follows:
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.