1. Statistical Institute and Computerized Information Systems, Faculty of Business AdministrationUniversity of Puerto Rico, Río Piedras Campus 15 AVE Unviversidad STE 1501 San Juan 00925‐2535 PR USA
2. Department of Mathematics, Faculty of Natural SciencesUniversity of Puerto Rico, Río Piedras Campus 17 AVE Universidad STE 1701 San Juan 00925‐2537 PR USA