With excess return it states that its what the bond investor receives for assuming credit risk. Then they have the equation which is:
Excess return≈ s×t - _(SD×_∆s)
From this we can see that as spread narrow (delta s is negative) that the excess return increases. I don’t understand why this would be the case. If spreads narrow, high yield bonds behave more like investment grade bonds. My thinking here is, then during a spread narrowing excess return would NOT increase (return we receive from assuming credit risk) because the two are behaving identically. But the equation states otherwise.
Thanks,