1 1Departamento de Matemáticas, Centro Universitario de Ciencias Exactas e Ingenierías (CUCEI), Universidad de Guadalajara, 44430 Guadalajara, Jalisco Mexico.
2 2Facultad de Telemática, Universidad de Colima, 28040 Colima, Colima Mexico.
3 3Epidemiology and Biostatistics and Statistics and Probability Departments, Michigan State University, 909 Fee Road, East Lansing, MI 48824 USA.
4 4Biometrics and Statistics Unit, International Maize and Wheat Improvement Center (CIMMYT), Apdo. Postal 6-641, 06600 Mexico City, Mexico.