Probabilistic Expert Systems

A. Introduction Module outline • Information, uncertainty and probability • Motivating examples • Graphical models • Probability propagation • The HUGIN system 7 6 5 2 3 4 1 Motivating examples • Simple applications of Bayes' theorem • Markov chains and random walks • Bayesian hierarchical models • Forensic genetics • Expert systems in medical and engineering diagnosis The 'Asia' (chest-clinic) example The results of a single chest X-ray do not discriminate between lung cancer and tuberculosis, as neither does the presence or absence of dyspnoea. A recent visit to Asia increases the risk of tuberculosis, while smoking is known to be a risk factor for both lung cancer and bronchitis. Shortness-of-breath (dyspnoea) may be due to tuberculosis, lung cancer, bronchitis, more than one of these diseases or none of them. +2 Visual representation of the Asia example-a graphical model