1. PhD, Department of Economics, Management and Sociology, University of São Paulo, Travessa Dona Eugenia 17, Apto 103, Piracicaba, Sao Paulo 13416218, Brazil.
2. Senior Professor, ‘Luiz de Queiroz’ College of Agriculture (ESALQ/USP), University of São Paulo, Av. Pádua Dias, 11 – Cx. Postal 9, Piracicaba, Sao Paulo 13418900, Brazil.