The Fund employs an indexing approach designed to track the performance of the S&P 0-7 Year National AMT-Free Municipal Bond Index. This Index measures the performance of the investment-grade, fixed-rate U.S. municipal bond market with maturities between one month and seven years as determined by the Index provider, S&P Dow Jones Indices LLC. This Index includes municipal bonds from issuers that are primarily state and local governments or agencies whose interest is exempt from U.S. federal income taxes and the federal alternative minimum tax (AMT) (excluding bonds issued by U.S. territories and commonwealths and certain other bonds as determined by the Index Provider). To be eligible for inclusion in the Index, each bond must have a rating of at least investment-grade, as determined by a nationally recognized statistical rating organization (NRSRO) (e.g., at least BBB by Fitch Ratings, Inc), the lowest rating will be used in determining if the bond is investment grade.