Implied volatilities and Transaction Costs

Using data that contain bid and ask quotes for both options and stocks, the analysis investigates the constant volatility assumption of the Black-Scholes model. The analysis adjusts for bid-ask spreads and finds evidence that is inconsistent with the constant volatility assumption. Instead, the results reveal a strong negative correlation between volatility and stock price, and they suggest that using a nonconstant volatility model such as the CEV model would be more appropriate to price long-term options. Finally, transaction costs associated with the dynamic hedge tend to increase with an option's maturity, but decrease as a percentage of the option's price.