The econometric challenge is to specify how the information is used to estimate and forecast the mean and variance of the return, conditional on the past information. Currently the most powerful known techniques used to estimate and predict the volatility on high frequency data belong to a family of generalized conditional autoregressive heteroskedastic (GARCH) models. The goal of such models is to provide a volatility measure like a standard deviation that can be used in financial decisions concerning risk analysis, portfolio selection and derivative pricing