The investment seeks to track the performance of a market-weighted mortgage-backed securities index. The fund employs an indexing investment approach designed to track the performance of the Bloomberg Barclays U.S. MBS Float Adjusted Index. This index covers U.S. agency mortgage-backed pass-through securities. To be included in the index, pool aggregates must have at least $250 million currently outstanding and a weighted average maturity of at least 1 year. All of the fund's investments will be selected through the sampling process, and under normal circumstances, at least 80% of the fund's assets will be invested in bonds included in the index.