If a positive CAT is equal to a negative CAT and negative CAT equals positive CAT then what is neutral CAT?

What do you mean by CAT? It usually stands for "computerized axial tomography" (as in 'CAT scan') but that is not capable of being positive or negative unless you mean it shows or does not show the presence of a given symptom of an illness.

I suppose you could say that a CAT scan which was "negative" in the sense that it found no signs of illness could be called "positive" in the colloquial sense that it was good news for the patient.

(Similar to the confusion caused by people taking up the systems engineering terms 'positive feedback' and 'negative feedback' and using them out of context to mean something quite different. 'Positive feedback' is a reaction to a change within a closed system which has the effect of magnifying the effect of the change, and so is often destructive, but the term also gets used to mean 'praise' which is usually the opposite).

Does this really belong under Science > alternative ?