Conclusion
PROM
Strong evidence supporting the conceptual structure and scoring approaches is fundamental to valid use of a PROM. The structural validity of the HidroQoL has been established in prior research. Using CTT and additional IRT/Rasch analyses, this study provided new evidence for the structural validity of the HidroQoL questionnaire using data from a phase III-b trial, thus helping to fill an important evidence gap for the HidroQoL. Overall, our findings support the dual structure of the HidroQoL allowing summation of scores to generate a single score, as well as calculation of separate domain scores for daily activities and psychosocial impacts. The findings are consistent with results of previous validation studies. Significant DIF was found which needs to be evaluated further in future studies.