The investment seeks daily investment results that correspond to the inverse (-1x) of the daily performance of the S&P MidCap 400®. The fund invests in derivatives that ProShare Advisors believes, in combination, should have similar daily return characteristics as the inverse (-1x) of the daily return of the index. 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 that factors in criteria such as liquidity, price, market capitalization and financial viability. It is non-diversified.