“…It is essentially a linear regression model with two independent error components: a two-sided term that captures random variation of the production frontier across firms and a one-sided term that measures inefficiency relative to the frontier. In recent decades, most studies about production, cost or profit efficiency have used the conventional SFM (see, e.g., [1,9,10,15,19,[22][23][24][27][28][29][30][33][34][35][36]). In all these studies, it is assumed that the onesided and two-sided error terms are independent.…”