To pursue its goal, the fund generally invests in securities that are included in the Bloomberg US Aggregate Bond Index. The index is a broad-based benchmark measuring the performance of the U.S. investment grade, taxable bond market, including U.S. Treasuries, government-related and corporate bonds, mortgage pass-through securities, commercial mortgage-backed securities, and asset-backed securities that are publicly available for sale in the United States. To be eligible for inclusion in the index, securities must be fixed-rate, non-convertible, U.S. dollar denominated and have one or more years remaining to maturity. The index excludes certain types of securities, including, bonds with equity type features (e.g., warrants, convertibles and preferreds), tax-exempt municipal securities, inflation-linked bonds, floating-rate issues, strips, private placements, U.S. dollar-denominated 25 and 50 par retail bonds, structured notes and pass-through certificates. The index is market capitalization weighted and the securities in the index are updated on the last business day of each month.