I was looking at comparisons of performance between some VIX ETFs/ETNs. Generally, over long periods, they are very close, with different decay rates of course. I.E. TVIX generally does 2x what VIXY does, which makes sense as TVIX is a 2x ETN and VIXY is a 1x ETF. But sometimes there performance differs DRAMATICALLY. Like in Marchish 2012. VIXY declined in value much, much more than TVIX (adjusting for their 2x versus 1x percentage). On March 19 for example, VIXY was down 5.81%, which adjusting to make it 2x would make it down 11.62%. So you think TVIX would be down roughly the same 11.62%. Was it? No, it was UP 1.76%! There are lots of days like this. Does anyone know why this is? ETF I understand hold the underlying VIX futures, and ETNs are based on the underlying VIX futures, so its seems they should be very, very close at all times (2x just holding twice the amount of futures). But they are not. What gives? And VIX during this time didn't even do anything crazy at all, so it wasn't some extreme situation or what not. Thanks!