The investment seeks daily investment results, before fees and expenses, that correspond to three times (3x) the daily performance of the S&P MidCap 400®. The fund invests in financial instruments that ProShare Advisors believes, in combination, should produce daily returns consistent with the fund's investment objective. The index is a measure of mid-size company U.S. stock market performance. It is a float-adjusted, market capitalization-weighted index of 400 U.S. operating companies and real estate investment trusts selected through a process. The fund is non-diversified.