The investment seeks to provide investment results that, before fees and expenses, correspond generally to the total return performance of an index derived from the oil and gas equipment and services segment of a U.S. total market composite index. In seeking to track the performance of the S&P Oil & Gas Equipment & Services Select Industry Index, the fund employs a sampling strategy. It generally invests substantially all, but at least 80%, of its total assets in the securities comprising the index. The index represents the oil and gas equipment and services segment of the S&P Total Market Index (S&P TMI).