Received: 14 May 2020
Accepted: 23 November 2020
First Online: 1 December 2020
Ethics approval and consent to participate
: The study was presented to the ethics committee of Philipps-Universität Marburg for an ethics approval. The ethics committee of Philipps-Universität Marburg decided that no ethics approval is necessary (reference number: ek_mr_06_05_20_geraedts) because all data used and analysed in this study are publically available secondary data of the German health care system. All data are irreversibly anonymised and censored according to German data protection regulations and no patient data are used in this study.
: Not applicable.
: WDC: The author declares that he has no competing interests.AO: The author declares that she has no competing interests.RAK: The author declares that she has no competing interests.MG: Declarations of interest: Max Geraedts has received payment from the German Medical Association for acting as a consultant on minimum volume. He has received honoraria for lectures on minimum caseloads and reimbursement of travel costs from the Federal Joint Committee (G-BA). The Federal Ministry of Health has supported his research on minimum volume.