If a datum's previous certainty factor is CFp and a new rule computes a certainty factor CFn, the combined certainty factor is given by:
cfcombine(CFp, CFn) =
| CFp + CFn * (1 - CFp) | CFp > 0, CFn > 0 |
| (CFp + CFn) | signs differ |
| / (1 - min(| CFp | , | CFn |)) | |
| - cfcombine(- CFp, - CFn) | CFp < 0, CFn < 0 |
This algorithm has a desirable feature: it is associative and commutative; therefore the result is independent of the order in which rules are considered.
A CF of + 1 or -1 is dominant and sets the combined CF to that value.