This dissertation presents methodological advances in the field of frailty models. Time to event data is very common in biomedical applications. Multivariate data, such as recurrent event... Show moreThis dissertation presents methodological advances in the field of frailty models. Time to event data is very common in biomedical applications. Multivariate data, such as recurrent event histories or clustered failures, typically require special modeling techniques. Frailty models extend the proportional hazards models by employing random effects. In this book, the first chapter represents an introduction to the field of frailty models. The second chapter studies the small sample properties of such models in more depth. In particular, it addresses the questions of identifiability of frailty models. The third chapter describes a score test that may be used to test whether a recurrent events process is associated with a terminal event. The fourth chapter studies the problem of event-dependent selection in the context of recurrent events data. This problem is relevant when the data are collected from registries. The fifth chapter introduces a novel R package and presents an overview of available software for estimating frailty models. Show less
The majority of platelet transfusions are given to patients with a hematological malignancy to prevent or treat bleeding complications. The adhered transfusion trigger for patients with an... Show moreThe majority of platelet transfusions are given to patients with a hematological malignancy to prevent or treat bleeding complications. The adhered transfusion trigger for patients with an increased risk of bleeding varies among hematologists. Although almost 20.000 donors are HLA typed in the Netherlands, adequate transfusion support cannot be guaranteed for all immunized patients, especially not for patients from a non-Caucasian background. From a clinical perspective, major hemorrhage is the most relevant outcome to measure effectiveness of platelet transfusions. We developed a model consisting of drop in hemoglobin, transfusion support, and CT-brain to enable the identification of major hemorrhage among leukemic patients in routinely recorded data. In the Netherlands, the standard platelet concentrate is derived from buffy coats and resuspended in plasma or platelet additive solution (PAS) and can be stored for seven days. Storage has a negative effect on safety and efficacy of platelet transfusions. Using routinely collected health care data, we demonstrated a lower risk of a positive blood culture after transfusion of platelet concentrates stored for five to seven days. Using the database of TRIP, we showed an increased risk of transfusion transmitted bacterial infections for platelet concentrates stored in PAS compared to those stored in plasma. Show less
