PO/IO positive, remember, college, shorter, where

jbaldyga

Don't think this was asked:

Reviewing what are typically lightly-tested topics (but, who knows).

"Hedging MBS": my notes say principal-only (PO) bonds have high positive duration, interest-only (IO) high negative duration - varies depending where you are on the curve (e.g. for PO's: is negative at shorter rates, positive at medium-to-long-term rates).

Why would PO's have positive duration? I vaguely remember this concept... not sure if was L1/L2, or maybe my college bond elective.