1. Faculty of Economics, University of Porto, 4200-464 Porto, Portugal
2. Faculty of Economics, University of Porto, CEF.UP, 4200-464 Porto, Portugal
3. Faculty of Economics, University of Porto, LIAAD/ INESC TEC, 4200-465 Porto, Portugal
4. Faculty of Economics, University of Porto, CEF.UP and OBEGEF 4200-464 Porto, Portugal