Price impact versus bid-ask spreads in the index option market

We investigate the puzzle of why bid-ask spreads of options are so large by focussing on the price impact component of the spread. We propose a structural vector autoregressive model for trades in the option market to analyze whether they move the underlying price and/or the underlying’s volatility. Our model captures cross-option strategies by pooling order flows across contracts after a decomposition into exposure to the underlying asset and its volatility. While our estimates confirm that S&P500 option trades indeed significantly move the underlying and the volatility, the economic magnitudes are very small. Hence, large bid-ask spreads of options remain a puzzle