The investment seeks to track the investment results of the Russell Midcap Index, which measures the performance of the mid-capitalization sector of the U.S. equity market. The fund generally invests at least 80% of its assets in the component securities of its underlying index and in investments that have economic characteristics that are substantially identical to the component securities of its underlying index (i.e., depositary receipts representing securities of the underlying index) and may invest up to 20% of its assets in certain futures, options and swap contracts, cash and cash equivalents.