Formally, given a set of n DMUs (DMUr, r = 1,2, …p, …n) each one consuming m inputs (x1r, x2r, …, xmr) to produce s outputs (y1r, y2r, …, ysr), the input oriented efficiency θp* of unit p, is given by the solution of the following linear programming problem: θp*=max∑j=1sujpyjp−wp, p ∈ {1,2,…,n}.