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12
Decisions involving groups
of individuals
Introduction
This book has spent many chapters looking at the use of decision analysis
for improving decision making. As we have seen, the major inputs to the
analysis are subjective probabilities, utilities and decision tree structures.
So far, we have focused on the individual decision maker, but important
decisions are often made by accountable managers working within
small groups of people, most, or all, of whom have information that
could be utilized in the decision-making process. Often individuals
may differ in their subjective probabilities of events, their utilities of
outcomes or in their perception of the subsequent actions available
as the pattern of actions, events and outcomes is unfolded into the
future.
If the opinion and values of individuals differ, how should the differences
be resolved? Obviously, several individuals who are involved in
decision making bring together a larger fund of experience, knowledge
and creative insights. It is intuitively reasonable that the chances of overlooking
possible events and possible courses of action are diminished in
group decision making. Indeed, the synergy of individuals may make
the overall quality of the group decision greater than the sum of the
parts. The creation of juries, panels and cabinets as ways of reaching
decisions can be seen to be based on this premise.
This chapter describes and evaluates ways of combining individual
judgments to produce ‘improved’ judgments. There are essentially two
approaches to the problem: mathematical and behavioral aggregation
(although the approaches can be combined). Mathematical aggregation,
which we will discuss first, involves techniques such as the calculation
of a simple average of the judgments of the individual group members.
In behavioral aggregation a group judgment is reached by members of
the group communicating with each other either in open discussion or
via a more structured communication process.