Certainty Factor Meaning

Traditional probability values are on a scale of 0-1. Shortliffe argues this does not support ``ruling out'' reasoning of the kind done in medicine.

EMYCIN CF's are on a scale of -1 to +1. A CF combines both a ``positive probability'' and a ``negative probability''.

MB 0 - 1 Measure of Belief
MD 0 - 1 Measure of Disbelief
CF = MB - MD -1 to 1 Certainty Factor
-1 Definitely False
0 No information, or cancellation
+1 Definitely True

When a data parameter is True/False, ``False'' is represented as ``True'' with a CF of -1.

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