230 Chapter 8 METHODOLOGICAL LIMITATIONS While this thesis provides useful insights into the measurement of patientreported outcomes, patient experiences with patient-reported outcome measurement and variation in care provision for patients with inherited bleeding disorders, this thesis has several limitations which should be considered when interpreting the findings. These limitations are primarily related to the study population and the challenges experienced during the implementation and evaluation of VBHC. Study populations The studies mainly included adults and patients with von Willebrand disease Patients, caregivers, and healthcare professionals were included in different studies in this thesis to gain insight into the added value of the implementation of VBHC in the care for patients with inherited bleeding disorders. To identify which health outcomes are important for patients with inherited bleeding disorders and how to measure these important health outcomes, I performed a systematic literature review (Chapter 2), a Delphi study (Chapter 3) and a PROMIS validation study (Chapter 5). For all these studies, I aimed to include a representative sample of patients with von Willebrand disease, inherited platelet function disorders and rare bleeding disorders to ensure that the results would be applicable for the whole patient population. During study execution, difficulties were encountered in including enough participants. Even though we approached both children and adults to participate in our PROMIS validation study, only adults responded to the invitation. I was therefore unable to assess if the PROMIS instruments are also suitable to measure patient-reported outcomes in children with von Willebrand disease, inherited platelet function disorders and rare bleeding disorders. In addition, recruitment difficulties led to the inclusion of primarily patients with von Willebrand disease. This hindered my ability to determine which health outcomes are important for each separate group of inherited bleeding disorders. Moreover, I was unable to assess if the PROMIS instruments adequately measure the relevant patient-reported outcomes separately for patients with von Willebrand disease, inherited platelet function disorders and rare bleeding disorders. Furthermore, the PROMIS validation study primarily included patients with a non-severe bleeding tendency which might limit the generalizability of our findings. Previous research has, however, found that the health-related quality of life of patients with severe von Willebrand disease is
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