Based on your financial expertise, provide your response or viewpoint on the given financial question or topic. The response format is open.

Is there difference in risk between physical or synthetic replication of an index by an ETF?
First, make sure you understand the objective of an ETF.  In some cases, they may use leverage to get a multiple of the index's return that is different than 1.  Some may be ultra funds that go for double the return or double the inverse of the return and thus will try to apply the appropriate leverage to achieve that return. Those that use physical replication can still have a small portion be used to try to minimize the tracking error as there is something to be said for what kind of tracking error do you accept as the fund's returns may differ from the index by some measure. Yes.  For example, if you were to have a fund that had a 50% and -50% return in back to back periods, what would your final return be?  Answer: -25%, which if you need to visualize this, take $1 that then becomes $1.50 by going up 50% and then becomes $.75 by going down 50% in a compounded fashion.  This is where you have to be careful of the risks of leverage as those returns will compound in a possibly negative way.