September 1st, 2009, 9:58 pm
The gama portion is predictable. Short ETFs and levered ETFs are all short gamma due to their one day return horizon (they need to be rehedged daily). However, the end of day trade for a levered or short ETF is the sum of the gamma and the contribution withdrawal activity. It is the contributions and withdrawals that are unpredictable. If they offset the gamma, you won't know until it is too late.