The investment seeks to track the investment results of an index composed of mid-capitalization U.S. equities. The fund generally invests at least 90% of its assets in securities of the underlying index and in depositary receipts representing securities of the underlying index. The underlying index measures the performance of the mid-capitalization sector of the U.S. equity market. The underlying index is a float-adjusted, capitalization-weighted index of the 800 smallest issuers in the Russell 1000® Index.