Nikolaos Kourogenis University of Piraeus   80 Karaoli & Dimitriou str Piraeus, 18534 Greece   nkourogenis@yahoo.com   http://web.xrh.unipi.gr/index.php?option=com_content&task=view&id=31&Itemid=76&lang=en           JEL Areas: C2 : Single Equation Models; Single Variables: General C1 : Econometric and Statistical Methods: General