First Author:   Helton Saulo Department of Economics - Federal University of Rio Grande do Sul / Porto Alegre, RS, Brazil development20@gmail.com   development20@gmail.com Porto Alegre, 90010-350, Brazil   +55532121376(Phone) +55532121376(Fax) Second Author: Jeremias Leao Department of Mathematics - Federal University of Piaui / Picos, PI, Brazil ms.statistic@gmail.com   Picos