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|
|0||No information, or cancellation|
When a data parameter is True/False, ``False'' is represented as ``True'' with a CF of -1.
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