191 Psychometrics of the pediatric PROMIS measures in hemophilia High floor and ceiling effects implicate that distinctive items are missing at the ends of the scale, making it difficult to distinguish patients with few or no complaints from each other [44], which results in an unreliable measurement for these patients. This also may explain the low reliability for the PROMIS Mobility Item bank. 4.2 Health Related Quality of Life The results of this study showed that the HRQoL of boys with hemophilia is comparable to the Dutch general population, except for the domains Pain Interference and Mobility. The high HRQoL found in this study is comparable to other studies assessing the HRQoL of boys with hemophilia with the legacy instruments [9,10,42]. Boys with a severe phenotype of hemophilia in the Netherlands experience few joint bleeds because the annual bleeding rate is low due to adequate prophylactic therapy. It is therefore recommended to repeat this study in a group of boys with hemophilia in low-income countries with less access to effective treatment. A limitation of this study is that as a measure of sociocultural determinants of the population, we did not have information on the race or ethnicity of participants, but did present information on place of birth of parents as a proxy for this. 4.3 Future research The number of the PROMIS CAT items administered was still relatively high. The reason for this is that available items on the high or low end of the scale are limited and more difficult to measure reliably. Consequently, patients with no problems or complaints have to answer the maximum amount of items to reach the CAT stopping rule (SE ≤ 3.2 and/or a maximum of 12 items). To reduce the burden of administration of PROMs for patients, initiatives are currently exploring the possibility to optimize these CAT stopping rules [55]. There also have been initiatives to shorten the legacy instruments [56,57]. Conclusion The PROMIS pediatric measures are reliable and feasible to use in hemophilia clinical care and research. Although, more research is needed to further reduce the burden of completing PROMs and to get more insight into the minimal important changes in patients with hemophilia. Innovative therapies are currently implemented of researched in clinical trials [4,5]. The need for reliable and valid instruments is crucial to measure the impact and cross-benefit of these innovative treatments. We conclude that the PROMIS measures are valid alternatives to the well-known legacy instruments, and importantly 7
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