Page 146 - DCAP310_INTRODUCTION_TO_ARTIFICIAL_INTELLIGENCE_AND_EXPERT_SYSTEMS

Introduction to Artificial Intelligence & Expert Systems

Notes
Example: Producing Counter-intuitive Results in Case of Low Conflict

The following example shows where Dempster’s rule produces a counter-intuitive result, even
when there is low conflict.
Suppose that one doctor believes a patient has either a brain tumor, with a probability of 0.99, or
meningitis, with a probability of only 0.01. A second doctor also believes the patient has a brain
tumor, with a probability of 0.99, and believes the patient suffers from concussion, with a
probability of only 0.01. If we calculate m (brain tumor) with Dempster’s rule, we obtain
m(brain tumor) = Bel(brain tumor) = 1.
This result implies complete support for the diagnosis of a brain tumour, which both doctors
believed very likely. The agreement arises from the low degree of conflict between the two sets
of evidence comprised by the two doctors’ opinions.
In either case, it would be reasonable to expect that:

m(brain tumor) < 1 and Bel(brain tumor) < 1.
Since, the existence of non-zero belief probabilities for other diagnoses implies less than complete
support for the brain tumour diagnosis.

Self Assessment

State whether the following statements are true or false:

5. The KR can be made to be dependent of the underlying knowledge model or knowledge
base system (KBS) such as a semantic network.
6. The more expressive a KR, the complex and more compact it is to express a fact or element
of knowledge within the semantics and grammar of that KR.
7. There is only one KR techniques.
8. Belief in a hypothesis is constituted by the sum of the masses of all sets enclosed by it.

7.3 The Dempster – Shafer Theory

Potential computational complexity problems
(i) It lacks a well-established decision theory whereas Bayesian decision theory maximizing
expected utility is almost universally accepted.

(ii) Experimental comparisons between D – S theory and probability theory seldom done and
rather difficult to do; no clear advantage of D – S theory shown.

7.3.1 Characteristics of D – S

The public also relies on specific heuristics to form opinions about science and science news.
Scientists and communicators often assume that the public objectively accumulates and evaluates
scientific information to develop opinions, but research has shown heuristics have a larger
effect than specific science knowledge.

Example: A 2007 study examined how people in the United States developed opinions
about agricultural biotechnology. Their results showed that the public used key heuristics to

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