[Staffing levels and patient-related outcomes : Systematic literature review on international evidence].

The objective of this study was to systematically review the international literature with respect to significant links between staffing levels or qualification on the one hand and patient-related outcomes on the other. Of the initial 7778 abstracts identified by means of a complex search strand in PubMed and CINAHL, 51 could finally be included in a qualitative synthesis. A total of nine different patient-related outcome categories with significant associations on an at least ordinally scaled level were distinguished. None of the studies included had a (quasi-)experimental research design. Despite, in some instances, high numbers of cases at multiple sites and efforts to control obvious confounding variables by regression analysis, no evidence-based conclusions for health policy or clinical practice can be drawn from the available observational studies. There is therefore a considerable need for prospective randomized or at least quasi-experimental studies also as accompanying research on novel models of financing.