%A XU, Jin %A ZERVOPOULOS, Panagiotis D. %A QIAN, Zhenhua %A CHENG, Gang %D 2012 %T A UNIVERSAL SOLUTION FOR UNITS - INVARIANCE IN DATA ENVELOPMENT ANALYSIS %K %X The directional distance function model is a generalization of the radial model in data envelopment analysis (DEA). The directional distance function model is appropriate for dealing with cases where undesirable outputs exist. However, it is not a units-invariant measure of efficiency, which limits its accuracy. In this paper, we develop a data normalization method for DEA, which is a universal solution for the problem of units-invariance in DEA. The efficiency scores remain unchanged when the original data are replaced with the normalized data in the existing units-invariant DEA models, including the radial and slack-based measure models, i.e., the data normalization method is compatible with the radial and slack-based measure models. Based on normalized data, a units-invariant efficiency measure for the directional distance function model is defined. %U https://journals.aserspublishing.eu/tpref/article/view/1173 %J Theoretical and Practical Research in Economic Fields %0 Journal Article %P 121-128%V 3 %N 2 %@ 2068-7710 %8 2012-12-31