Computing a Joint Entry

Assume a new event T (class starts at 9h15).

How to compute an entry in a joint distribution?

• What is P(S ^ ~M ^ L ^ ~R ^ T)?

The general case

So any entry in joint pdf table can be computed. And so any conditional probability can be computed.

Case Study’s

Pathfinder system. (Heckerman 1991, Probabilistic Similarity Networks, MIT Press, Cambridge MA).

• Diagnostic system for lymph-node diseases.

• 60 diseases and 100 symptoms and test-results.

• 14,000 probabilities.

• Expert consulted to make net.

  • 8 hours to determine variables.

  • 35 hours for net topology.

  • 40 hours for probability table values.

• Apparently, the experts found it quite easy to invent the causal links and probabilities.

• Pathfinder is now outperforming the world experts in diagnosis. Being extended to several dozen other medical domains.