ProShares UltraPro Short MidCap400 ETF is an exchange traded fund, which seeks daily investment results, which correspond to triple (300%) the inverse (opposite) of the daily performance of the S&P MidCap 400 Index. The ETF seeks a return of -300% of the return of an index (target) for a single day. The S&P MidCap 400 Index is a used measure of mid-size company United States stock market performance. Companies are selected for inclusion in the Index by Standard & Poor's based on adequate liquidity, appropriate market capitalization, financial viability and public float. It is not possible to invest directly in an index.