On the Intraday Relation between the VIX and its Futures

We study the intraday dynamics of the VIX and VXF for the period January 2, 2008 to December 31, 2012. Applying a Vector Autoregression (VAR) model on daily data, we observe some evidence of causality from the VXF to the VIX. However, estimating a VAR using our ultra-high frequency data, we find strong evidence for bi-directional Granger causality between the VIX and the VXF. Overall, this effect appears to be stronger from the VXF to the VIX than the other way around. Impulse response functions and variance decompositions analysis further confirm the dominance of the VXF. Lastly, we show that the causality from the VXF to the VIX has been increasing over our sample period, whereas the reverse causality has been decreasing. This finding suggests that the VIX futures have become increasingly more important in the pricing of volatility. We further document that the VIX futures dominate the VIX more on days with negative returns, and on days with high values of the VIX, suggesting that on those days investors use VIX futures to hedge their positions rather than trading in the S&P 500 index options