Homogeneity of the German diagnosis-related groups.

This study analysed the outstanding homogeneity of the German Diagnosis-Related Groups (G-DRG) using the reduction in variance (R²) of costs. Arbitrary increase in case groups, definition of additional charges and combination of several case groups in one DRG were considered as potential confounders. In 2009, the G-DRG-system offers an outstanding homogeneity with R² of 83.5% in comparison to 2004 with R² of 70.2%. The effect of an arbitrary increase in case groups is negligible. However, a simulation of the other confounders explains three-fourth of the increase in R² between 2004 and 2009. The definition of additional charges attributes in particular to the outstanding homogeneity. The assessment of DRG-systems with R² should be complemented with measures that are independent from a trimming of costs, e.g. relating actual costs with prospective payment. The G-DRGs left medical ground in order to achieve optimal economical homogeneity.