Villano, R. A., and C.-D. T. T. Tran. “Technical Efficiency Heterogeneity of Tertiary Institutions in Viet Nam: A Metafrontier Directional Technology Approach”. Technological and Economic Development of Economy, Vol. 25, no. 6, Sept. 2019, pp. 1058-80, doi:10.3846/tede.2019.7452.