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Some final words of advice 455
Questions relating to the validity of expert systems have often not
been asked. Most often expert system researchers have been concerned
with problems of redundancy, conflicts, circularity (e.g. self-referencing
chains of inference) and incompleteness in rule sets. 56 When the validity
issue is analyzed the level of analysis is usually a comparison of the
expert’s and the completed expert system’s decisions or advice when
both are presented with example cases. The resulting error rate, i.e.
the proportion of ‘incorrect’ decisions or advice given by the system, is
often summarized by a simple percentage count. However, as we have
seen in our discussion of linear models, human judgment contains a
random error component. The benefit of linear modeling is elimination
of this error by averaging techniques. Hence the incremental validity of
the model of the judge over the judge’s holistic decisions/predictions.
Methods of validating expert systems have not, to date, been able
to systematically identify and extract the random error component
in human judgment. The only method at the knowledge engineer’s
disposal with which to identify such a component within the expert
system representation of the expert’s knowledge is to ask the expert to
introspect on the rule set.
Some final words of advice
If you have a decision problem – one that is difficult and important so
that you are planning to use decision analysis to give you guidance
and insights – then how should you approach the problem? Could you
be solving the wrong problem? How much effort should you devote
to the analysis? In this final section, we give advice on the way to use
decision-aiding techniques to approach decision problems.
It is all too easy to rush into making a decision. Difficult unresolved
decisions can be uncomfortable to live with so that there is often a
desire for speedy action. Indeed, in some organizations, the person who
makes speedy decisions may be regarded as strong and decisive, while
more cautious colleagues may be seen as weak and vacillating. Even
if there is no time pressure on the decision maker, old habits, narrow
vision, preconceptions and overconfidence may lead to the decision
being made without spending time to step back and take a broad view
of the problem.
The use of one, or other, of the decision-aiding techniques we have
described in this book might reduce these dangers, but it will not