Villano, Renato A., and Carolyn-Dung Thi Thanh 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, https://doi.org/10.3846/tede.2019.7452.