mean well if they're both together bigger and together smaller then this will always be a positive quantity and will have a positive number come out if one of them tends to be bigger when the other one is smaller and the other way around then they'll have opposite signs a negative entry will come out and they're completely independent and their bigger is smaller then I'll cancel it be 0 so Sigma IJ is positive when they both together tend to be above average negative when they have counter correlation in terms of above below