[Controversial study results in relation to minimum volume standards]

Multiple studies have demonstrated positive associations between volume and treatment outcome, especially in complex procedures. However, using these results in determining volume standards in Germany keeps being problematic: often, there is a lack of specific German data on the volume and outcome of healthcare providers making the modeling of potential effects almost impossible. In addition, recent publications focusing on the methods that are typically used in analyzing these associations indicate that the significance of positive volume-outcome associations is limited. The methodological quality of most studies is rather low, and there is a high heterogeneity among them concerning study populations, case mix, study designs and analytical methods. Results on the single-hospital level show a high variation of outcome parameters. There are both good hospitals with low volumes and bad hospitals with high volumes. Using the "best guideline-based current procedures" seems to be of high importance for the good outcomes of small and big hospitals. Furthermore, studies have demonstrated that data on historical outcomes are a better predictor for good outcomes than hospital procedural volumes. Furthermore in some studies negative outcomes were shown to be related to high volumes at facilities with a high case load per staff member. These results suggest that a more sophisticated consideration of the methods and results of volume-outcome studies is required. Therefore, volume standards should continue to be cautiously applied and obligatorily accompanied by health services research.