As explained in the previous section, existing methods fail to accommodate the adverse effects of the eco-variables viz; CO2 emissions, in the DEA model. In this section, we propose a new approach to deal with undesirable outputs.
This method takes into account the impact rate of the undesirable output on the efficiency score. Accordingly, the intensity of the impact, or the influence of the undesirable output, is considered as a negative output that leads to a decrease in efficiency scores. The whole idea can be expressed as follows: