The investment seeks daily investment results, before fees and expenses, that correspond to three times the inverse (-3x) of the daily performance of the S&P MidCap400®. The fund invests in derivatives that ProShare Advisors believes, in combination, should have similar daily return characteristics as three times the inverse (-3x) of the daily return of the index. The index is a float-adjusted, market capitalization-weighted index of 400 U.S. operating companies and real estate investment trusts selected through a process that factors criteria such as liquidity, price, market capitalization and financial viability. The fund is non-diversified.