1. Institute of Computer and Systems Engineering of Coimbra, Rua Antero de Quental 199, 3000-033 Coimbra, Portugal
2. Department of Business and Economics, Beira Interior University, Estrada do Sineiro, 6200-209 Covilhã, Portugal
3. Faculty of Economics, Coimbra University, Avenida Dias da Silva 165, 3004-512 Coimbra, Portugal