The investment seeks to track as closely as possible, before fees and expenses, the total return of the Dow Jones U.S. Mid-Cap Total Stock Market IndexSM. The fund invests at least 90% of net assets in stocks that are included in the index. The index includes the mid-cap portion of the Dow Jones U.S. Total Stock Market Index actually available to investors in the marketplace. The Dow Jones U.S. Mid-Cap Total Stock Market Index includes the components ranked 501-1000 by full market capitalization. The index is a float-adjusted market capitalization weighted index. It may invest up to 10% of its net assets in securities not included in its index.