ETF: « Exchange-traded funds (or ETFs) are open ended mutual funds that can be traded at any time throughout the course of the day. Typically, ETFs try to replicate a stock market index such as the S&P 500″ –wikipedia
Proshares UltraShort DJ30: « The UltraShort Dow30 ProShare seeks daily investment results, before fees and expenses, that correspond to twice (200%) the inverse (opposite) of the daily performance of the Dow Jones Industrial Average Index ».
before fees and expenses since opening on 07/30/07
ETF on SP500 = -0.5%
PS US DJ30 = -1.4%
APPL = -6.5%