convexity is negative = at low interest rates?

CFA Level II Fixed Income
#1

How so?

#2

Only for callable bonds because as interest rates drop issuers would rather call the bonds and reissue them at the lower market rates

#3

For an MBS too, as people refinance mortgages at lower interest rates, a.k.a. “prepayment risk”

#4

Use the convexity formula on a low yielding callable bond and you’ll see a negative sign ;), but not dobwith putable or straight.