GBF excludes securitized debt from a broad-market allocation to investment-grade USD-denominated debt. The reweighting of the remainder of the US bond market pumps up GBFs exposure to Treasurys and corporate debt, which together make up over 80% of GBFs assets. The fund delivers near-perfect exposure to the broader market in terms of portfolio weighting, yield, credit rating, and duration. GBF excludes certain special issues such as targeted investor notes, state and local government series bonds and coupon issues that have been stripped from bonds. The underlying index is reconstituted monthly. GBF uses a representative sampling index strategy which purchases a subset of securities that matches the return and risk characteristics of the Underlying Index.