CRS takes into account multiple inputs that are used in the production process to generate
outputs and yields our measures of total factor productivity (TFP) a score including all factors
of productions. The DEA input approach defines the frontier by seeking for the maximum
possible reduction in input usage, with output held constant, vice versa. DEA can be
estimated either as input-oriented or output-oriented index. The two results of both measures
give the same technical efficiency scores when constant returns to scale is assumed. In this
paper, an input-oriented measure using CRS is assumed because the DMUs want to minimize
their inputs to achieve given outputs using production function. DEA measures are obtained
by introducing a ratio of M outputs over N inputs, as follows: