The development of the prediction model will take place in cooperation with several experts, including prof. dr. J.G. van der Bom, professor in clinical transfusion medicine, and prof dr. H. Putter, professor of medical statistics and an expert in dynamic prediction modelling. We will develop a dynamic prediction model using landmarking, as described elsewhere.(12) A statistical analysis plan will be written and signed prior to any analysis. Variables to be included in the model will be chosen prior to the statistical analyses.