Category Archive: Frequently Asked Question


A factor which describes the amount of goods, services or other outcome obtained as a result of the processing of resources. Also, any factor which describes the qualitative nature of the resulting outcome.

Overall efficiency

Same as aggregate efficiency


Short for decision making unit or DMU.


In an output-oriented model, an inefficient unit is made efficient through the proportional increase of its outputs, while the inputs proportions remain unchanged.


The requirement that the relationship between inputs and outputs not be erratic. Increasing the value of any input while keeping other factors constant should not decrease any output but should instead lead to an increase in the value of at least one output.

Multiplier form

Associated with each DEA model type (eg CCR, BCC) is both a primal and dual formulation. To avoid confusion over which formulation is primal and which dual, the multiplier form is always understood to refer to the formulation involving virtual multipliers (Ali and Seiford 1993). [Ali A and Seiford L (1993), ‘The mathematical programming approach …

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Window analysis

Tabular method for examining the changes in the efficiencies of a set of units over time. A set of time periods (1 ..t) is chosen and the efficiency of each unit (1..n) is computed separately for each period so that the efficiency of a given unit over each period is treated as a new unit …

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The input and output values that would render an inefficient unit relatively efficient. Thanassoulis and Dyson (1992) examine ways of modifying the DEA model so as to set priorities over which targets should be improved. [Thanassoulis E and Dyson R G (1992) ‘Estimating preferred target input-output levels using data envelopment analysis’, J. of Opi. Res., …

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Well-rounded performance

If a DMU is rated efficient and more or less equal importance has been given to each of its factors, it is said to exhibit well-rounded performance.

Reference set

The set of efficient units from which an inefficient unit’s inefficiency has been determined. Originally, the term was used to denote the set of all units in the analysis (i.e. the field) and the set of efficient units was known as a reference subset, a term still used by some.

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