- When to decide confidence is too low for rule to apply
- How to compute certainty factors in rules

- Values below threshold indicate conclusion is too uncertain to hold, so rule not used
- Values above threshold indicate conclusion has acceptable certainty

- Rules state that a conclusion applies with given confidence, given hypotheses.
- What confidence should be concluded if hypotheses are not completely certain?
- Also, what confidence should be concluded if rule has multiple hypotheses, each of which is not fully certain?

Here is one approach, patterned after TMycin by Gordon Novak

Proceed in 2 steps

- Determine confidence in rule conditions being met
- Base confidence on rule conclusions on condition confidence and rule confidence factor

- If only one factor in condition, that gives the confidence
- If several factors, connected with OR, take maximum confidence
- If several factors, connected with AND, take minimum confidence

- Multiply rule confidence by hypothesis confidence

- Computed certainty factors can get low quickly, so one must be somewhat careful in choosing thresholds
- A threshold confidence of 0.2 or so may be appropriate!

created May 13, 2003last revised May 13, 2003
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