A rational approach to investing is manifested through the realization of a higher yield for a given level of risk, and the realization of a given yield by accepting lower risk levels. Through the investment process, the question that is brought to investors’ attention is the importance of...

For proper valuation of risk to which the portfolio of financial assets is exposed, it is necessary to forecast the second moments of financial time series, that is variabilities. The empirical investigations show that financia time series are heteroskedastic, i.e. their volatility is not...