CONSTRUCTION, VALIDATION AND UPDATING OF A PROGNOSTIC MODEL FOR KIDNEY GRAFT-SURVIVAL

The construction, validation and updating of a prognostic model for kidney graft survival is reported using data from the Eurotransplant database. First, a model is constructed for data from transplantations in the period 1984 to 1987. The model is later updated for the 1988-1990 data. The first data set was randomly split into a training set (two-thirds of the data) and a validation set (one-third). To prevent overfitting empirical Bayes estimation of the transplantation centre effect was employed. After that, the validation set was used for fine-tuning by shrinkage. For updating with the 1988-1990 data parametric models were used after suitable transformation of the time axis; it appeared that survival had slightly improved. This necessitated a correction of the parameters in the exponential model. Correctness of the model was checked by extension to a Weibull model. The lack of fit was statistically significant, but practically ignorable. Recommendations are made to place less emphasis on the selection of variables and cut-off points, and more emphasis on the fine-tuning of the prognostic model by means of low-dimensional parametric models in independent data sets.