1. Department of Hematology, West German Cancer Center University Hospital Essen, University of Duisburg‐Essen Essen Germany
2. Department of Bone Marrow Transplantation, West German Cancer Center University Hospital Essen, University of Duisburg‐Essen Essen Germany
3. Rheinisch‐Westfälisches Institut für Wirtschaftsforschung Essen Germany