What is the smallest number of units I can use DEA for?
Although it works best with larger numbers of units, DEA can successfully work with a very small number of units but you cannot use many input/output factors if it is to be useful. There is a simple rule of thumb: Multiply the number of inputs by the number of outputs – that is the number of units that are likely to be given a score of 100%. So, with four inputs and four outputs, you’ll probably get 16 efficient units. If you have 20 units, the discrimination will not be very good! If you have 200 units, then there is no problem. Frontier Analyst® provides additional (non-DEA) analysis such as correlation displays so that you can view your data and select the input/output factors that you will use in the analysis. For example, if two inputs are highly correlated, then they perhaps represent the same thing and one could be excluded from the analysis.
