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

# Category: Frequently Asked Question

## 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 …

## 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 …

## Targets

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., …

## Virtual input(output)

Virtual input is obtained for each input by taking the product of the input’s value and its corresponding optimal weight as given by the solution to the primal model. Virtual outputs are obtained analogously. A virtual input or output describes the importance attached to the given factor. The virtual inputs always add up to the …

## Most productive scale size (MPSS)

MPSS is a unit (point) on the efficiency frontier that maximises the average productivity for its given input-output mix and after which decreasing returns to scale set in. See Banker & Kemerer (1989) on how to compute the MPSS. [Banker R and Kemerer C (1989) ‘Scale economies in new software development’, IEEE Trans. On Softw. …