Comparing the Productivities of Two Units At Two Different Points in Time

To remove the difficulty caused by different costs of the frontiers for calculating the changesof cost efficiency and its components, tohidi, et al [g. tohidi, s. razavyan, s. tohidnia,a global cost malmquist productivity index using data envelopment analysis, journal ofthe operational research society, 63 (2012) 72-78] proposed a global cost malmquist productivityindex. this index is applicable when input costs are known and producers aregoing to minimize the cost of decision making units (dmus). in this paper the aboveproposed index is generalized to compare the productivity of two different units at twodifferent points of time under the constant returns to scale (crs) and variable returns toscale (vrs). the global cost malmquist productivity index developed here is unique andis computed using nonparametric linear programming models, known as data envelopmentanalysis (dea). to illustrate the generalized index and its components, a numerical exampleat three successive periods of time is given.