William G. De Leon & Ravi K. Mattu penned a duration ditty for Pimco's April 2012 Viewpoint Series:
"Decoding Duration To Better Understand Your Portfolio"
This standard MBA level coursework post on duration has one statement that lacks robustness.
Ironically, under the heading of "Duration Isn't So Simple" the authors say that one of their four most important factors in assessing interest rate risk is ; "Bonds with default risk have a shorter duration than that implied by their stated maturity."
This last statement ignores bankruptcies or restructurings that lead to longer duration lower coupon debt replacements and it ignores debt re-structured into equity whose duration is arguably much longer than any of the firm's debt. Of course, junk rated issuers, who are by default the most prevalent cohort for these re-structuring/bankruptcy event prone issues, one could argue their equity duration will be much shorter than that of equity in general.