Mispricing of S&P 500 Index Options

   (290 K)

Widespread violations of stochastic dominance by one-month S&P 500 index call options over 1986-2006 imply that a trader can improve expected utility by engaging in a zero-net-cost trade net of transaction costs and bid-ask spread. Although pre-crash option prices conform to the Black-Scholes-Merton model reasonably well, they are incorrectly priced if the distribution of the index return is estimated from time-series data. Substantial violations by post-crash OTM calls contradict the notion that the problem primarily lies with the left-hand tail of the index return distribution and that the smile is too steep. The decrease in violations over the post-crash period 1988-1995 is followed by a substantial increase over 1997-2006 which may be due to the lower quality of the data but, in any case, does not provide evidence that the options market is becoming more rational over time.

Published: Review of Financial Studies, March 2009

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