Ruiz Vanoye, J.A., Díaz-Parra, O., Fuentes-Penna, A., Vélez-Díaz, D., García Munguía, M., Ruiz-Díaz, J. and Ruiz-Díaz, F. 2018. Motivation Index to Improve the Soccer Performance. International Journal of Combinatorial Optimization Problems and Informatics. 8, 3 (Jan. 2018), 45–57.