Joyciane C. Vasconcelos Master's Degree of Rural Economy/MAER of Universidade Federal do Ceará (UFC).   Av. Mister Hull, 2977 Bloco 826 Campus do Pici Fortaleza, Ceará 60.440-970/ 6017 Brasil   joyciane.c.v@gmail.com             JEL Areas: C : Mathematical and Quantitative Methods C2 : Single Equation Models; Single Variables: General