Efficiency is measured on a scale of 0 to 1, where a value of I indicates the unit is relatively efficient, and a value less than 1 indicates the unit is inefficient. The efficiency score of a unit will vary according to the factors and DMUs included in the analysis. In the early days of DEA, there was some concern as to whether it was justified to rank inefficient units according to their efficiency scores on the grounds that the scores may have been calculated from distinct reference sets.