The fund invests in financial instruments that ProShare Advisors believes, in combination, should produce daily returns consistent with the funds 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 that factors in criteria such as liquidity, price, market capitalization and financial viability. It is non-diversified.