Development of a core outcome set for studies on centralization of healthcare services

BACKGROUND: Centralization defined as the reorganization of healthcare services into fewer specialized units serving a higher volume of patients is a strategy to improve the outcome quality of medical procedures. Studies on centralization, however, tend to measure and report different outcomes impeding evidence syntheses. To advance research on the effects of centralization, this study aimed at developing a core outcome set (COS) for studies on centralization of hospital procedures. The envisaged COS should be generic and include all relevant outcomes irrespective of available data or measurement instruments. METHODS: For developing the COS, we conducted (1) a systematic review on the effects of minimum volume standards in hospitals, (2) a focus group study with patient representatives, (3) two interview studies with representatives of medical societies and statutory health insurance funds, (4) an online study with health services researchers, (5) the development of a longlist of outcomes and (6) a two-round Delphi study with all aforementioned participants. All interest-holder groups were based in Germany. The collected outcomes were categorized according to the Cochrane Effective Practice and Organisation of Care (EPOC) outcome taxonomy. A priori, we defined to include an outcome if ≥75% of all participants in a respective interest-holder group rated an outcome with 7-9 (critically important) on a 9-point Likert scale, and if this criterion was met by at least two interest-holder groups. RESULTS: In total, 61 participants took part in the focus groups (n = 14), the interviews (n = 28) and the online survey (n = 19). Of these 36 and 34 participated in Delphi I and II, respectively. From the studies, 48 outcomes were derived and presented in Delphi I. Based on participants' comments 45 outcomes were displayed in the Delphi II survey. The final COS comprises 27 outcomes in all EPOC outcome domains. Nine of these belong to the EPOC outcome domain "Outcomes related to the quality of care". CONCLUSIONS: Future studies on centralization should measure and report outcomes from a broad range of outcome domains, including outcomes in the domain "Quality of care". Instruments for measuring these outcomes need to be consented.