How Hero ATK and DEF stats affect units?

[NatashaQuick]

I am wondering about the blue parenthesis next to my troops' ATK and DEF stats. I was trying to figure out which artifact I wanted to equip when I realized that I have no idea what the blue numbers mean. I just can't make any sense of it.

What happened was I have an upgraded staff with +2 INT, and the Sword of Equilibrium that has just changed to the Sword of Darkness, which states that it has a -20% DEF to Elves and Humans effect. I didn't know if that meant the negative affects MY troops (which are Human), or the enemy troops, so I tried looking at their stats when it was equipped and when it wasn't. For some reason the blue numbers for my troops' ATK and DEF went down when I unequipped the sword??? Are the blue numbers supposed to be added to the basic stats of the troops in white to make a larger number than what is shown, or is it the base stat that isn't shown? I'm so confused and I'm probably trying to make this more complicated than it is. Thanks in advance!