183 Psychometrics of the pediatric PROMIS measures in hemophilia who achieved the lowest or highest possible score, respectively. A floor or ceiling effect was considered present if the commonly accepted threshold of 15% was exceeded [44,45]. Both the number of completed items as well as the floor and ceiling effects were compared between the PROMIS pediatric measures and the legacy instruments. 2.3.2. Construct validity To evaluate the convergent validity of the PROMIS pediatric measures, hypotheses regarding the correlations between the PROMIS pediatric measures and the legacy instrument were formulated by researchers of the project group (Table 1) and tested. Moderate correlations (Spearman’s rho, 0.40-0.69 [46]) were expected between PROMIS Pain Interference and Haemo-QoL Physical Health, PROMIS Depressive Symptoms and Haemo-QoL Feeling, PROMIS Mobility and PedHAL, and PROMIS Global Health and Haemo-QoL total score. Weak correlations (Spearman’s rho, 0.100.39 [46]) were expected between PROMIS Anxiety, PROMIS Anger and Haemo-QoL Feeling, and between PROMIS Peer Relationships and Haemo-QoL Other Persons. Although the constructs of these measures were closely related, the content differs due to the disease-specific vs. generic approach. Although no differences were expected between subgroups of boys with hemophilia based on previous literature [47,48], secondary analysis were performed comparing the mean PROMIS T-scores of the subgroups severe vs. non-severe (mild and moderate) hemophilia. 2.3.3. Outcomes To determine which PROMIS pediatric measures were relevant for patients with hemophilia, mean T-scores were calculated and compared with Dutch reference data [49-53] from the general male population (8-18 years) using independent t-tests. In addition, transformed/normalized total and scale scores of the legacy instruments were calculated. 2.4. Synthesis of the results Comparisons between the PROMIS pediatric measures and the legacy instruments are described regarding the number of completed items, floor and ceiling effects, and reliability. 7
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