Characteristics that are relevant in judging bond indices include: • The sample of securities: the number of securities in the index, and the criteria used to determine the specific bonds included in the index. • Market sector measured: indices can be composed of
government bonds,
municipal bonds, investment grade
corporate bonds, below-investment-grade (
high-yield bonds),
mortgage-backed securities,
syndicated or
leveraged loans. Indices may also consist of bonds within a certain range of maturities, e.g. long term, intermediate term, etc. • Weighting of returns: the impact of each individual issue's return on the overall index may be weighted by
market capitalization (the market value of the security), or equal-weighted for each security. Most bond indices are weighted by market capitalization. This results in the "bums" problem, in which less creditworthy issuers with a lot of outstanding debt constitute a larger part of the index than more creditworthy ones with less debt. • Quality of price data: the market price used for each bond in the index may be based on actual transactions, a brokerage firm's estimate or a computer model. • Reinvestment assumptions: what does the rate of return calculation assume regarding reinvestment of periodic interest payments from the bonds in the index? There are certain challenges inherent in constructing and maintaining a bond market index: • The bond market contains more individual securities than the stock market. A corporation which qualifies for inclusion in a particular bond index may have multiple bonds outstanding. • Most bonds are traded in a fragmented over-the-counter market that has no consolidated price quotation system. Therefore, unlike the stock market, there is no single source to consult to determine the definitive closing price of each bond in the index on any given day. • An individual bond's
duration changes with the passage of time remaining until maturity. This changes the index's price sensitivity to a given change in yield, even if the bonds comprising the index remain constant. A bond's
convexity and the value of any embedded options (e.g. call provisions) also change over time. == Indices and passive investment management ==