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.