review of the methods for evaluating congestion in dea and computing output losses due to congestion

data envelopment analysis (dea) is a branch of management, concerned with evaluating the performances of homogeneous decision making units (dmus). the performances of dmus are affected by the amount of sources that dmus used. usually increases in inputs cause increases in outputs. however, there are situations where increase in one or more inputs generate a reduction in one or more outputs. in such situations there is congestion in inputs or production process. in this study, we review the approaches that are available in the dea literature for evaluating congestion. also we introduce a model to compute output losses due to congestion. then, we present the results of the mentioned models on an empirical example and interpret the results.