Pricing Event Risk: Evidence from Concave Implied Volatility Curves

Abstract

We document that implied volatility (IV) curves extracted from short-term equity options frequently become concave prior to the earnings announcement day (EAD) reflecting a bimodal risk-neutral distribution for the underlying stock price. Firms with concave IV curves exhibit significantly higher absolute stock returns on EAD and higher realized volatility after the announcement, as compared to firms with non-concave IV curves. Hence, concavity in the IV curve constitutes an ex-ante option-based signal for event risk in the underlying stock. Returns on delta-neutral straddles, delta-neutral strangles, and delta- and vega-neutral calendar straddles are all negative and significantly lower in the presence of concave IV curves, showing that investors pay a substantial premium to hedge against the gamma risk arising due to this event.

Keywords: Earnings Announcement, Event Risk, Risk-Neutral Distribution, Implied Volatility Curve