2 variables x,y, the larger (x+y)/(x-y), the more is large-sum-small-difference of the variables involved. Or it can be (x+y)^m/(x-y)^n, where m,n>0, and preferably m,n>1. The greater m and n, the more is sensitivity.l you may take logarithm of this expression as well.
Thank you very much for your answer!But I still have a doubt,how should we call this indicator? Is there a term to describe it?like sum difference ratio(its a fake name) or something.