where, , , and are slack variables denoting input excess, output shortfall, and carry-over excess, respectively. This objective function is based on the input-oriented SBM model [59]. The main targets of evaluation of the objective function are excesses in both input resources and carry-over values. Since carry-over items have similar features as inputs, to be exact, a smaller amount is preferable to a larger amount, and both are accounted for in the objective function in a similar way. As observed from the constraint (2), carry-over items are those that have the role of connecting two consecutive terms. From model (1), it can be inferred that the efficiency of term t is measured by the relative slacks of inputs and carry-over items. Model (1) is thus the weighted average of term efficiencies over the whole terms