The investment seeks investment results that correspond generally to the price and yield performance, before fees and expenses, of the S&P National AMT-Free Municipal Bond IndexTM. The fund generally invests at least 80% of its assets in the securities of the underlying index and generally invests 90% of its assets in the securities of the underlying index and in securities that provide substantially similar exposure to the securities in the underlying index. The underlying index measures the performance of the investment-grade segment of the U.S. municipal bond market.