SPFF targets the 50 highest-yielding preferred stocks issued in the United States. Preferred stocks usually offer higher fixed-income payments than bonds with lower investment per share. It also has a priority claim over common stocks in the event of a company's liquidation. Holdings must meet minimum liquidity and size. The highest-yielding securities are ranked until the target count is reached. The fund uses a sampling method in tracking the index, which means it will invest in a sample of securities that collectively have an investment profile similar to that of the underlying index. The index is rebalanced semi-annually. Prior to Apr. 3, 2023, the fund tracked the S&P Enhanced Yield North American Preferred Stock Index.