PERFEX uses certainty factors to calculate the probability of everything it pronounces upon. In this case it is the certainty factor of whether or not this patient can be regarded as abnormal.
The certainty factors are in this case being translated to the following expressions:

  0.80  ->  1.00 :  is.
  0.40  ->  0.80 :  probably is.
  0.20  ->  0.40 :  possibly is.
 -0.20  ->  0.20 :  equivocally is.