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. It seeks to track the investment results of the S&P MidCap 400® (the "underlying index"), which measures the performance of the mid-capitalization sector of the U.S. equity market.