Dumas, Bernard J; Fleming, Jeff; Whaley, Robert E - C.E.P.R. Discussion Papers - 1996
Black and Scholes (1973) implied volatilities tend to be systematically related to the option’s exercise price and time to expiration. Derman and Kani (1994), Dupire (1994), and Rubinstein (1994) attribute this behaviour to the fact that the Black/Scholes constant volatility assumption is...