The EORTC QLQ-F17 as a shortened version of the EORTC QLQ-C30 to assess self-reported functioning in cancer patients: investigating equivalence and psychometric properties in a randomized cross-over trial

Background
The EORTC QLQ-F17, a shortened version of the EORTC QLQ-C30, solely contains the items related to functioning and omits symptom scales. The QLQ-F17 is conceived an equivalent to the functional part of the QLQ-C30, but to date there is no empirical evidence to support this rationale.
Methods
This randomized, cross-over, multi-national, questionnaire-based study investigates the equivalence and psychometric properties of the QLQ-F17 compared to the functional scales of the QLQ-C30. Respondents had to fill in both questionnaires, the order of which was presented in a randomized and balanced manner (QLQ-C30—QLQ-F17 vs. QLQ-F17—QLQ-C30). Equivalence testing used Differential Item Functioning (DIF) and linear models. The margin of equivalence was set at ]–5, 5[ points. The study is registered with ClinicalTrials.gov (NCT05479682). Patients were enrolled between February 17 and March 28, 2023.
Findings
A total of 2672 cancer patients of all major cancer types, aged between 18 and 92 years with an equal gender distribution (50/50) from 11 countries, were recruited between 17 February and 28 March 2023. Adjusted mean differences between QLQ-C30 and QLQ-F17 ranged between −1·55 and 3·25 for all scales, and the limits of the 95%-CIs, ranging from −3·11 to 4·87, were all within the equivalence margin. All effect sizes of the DIF analyses were <0·01. For the scales of the QLQ-F17, Cronbach's Alpha ranged from 0·73 to 0·89, item–own scale correlations from 0·47 to 0·78 and item–other scale correlations from 0·19 to 0·70.
Interpretation
The QLQ-F17 yielded score values that are equivalent to the functional part of the QLQ-C30. Consequently, future clinical studies can employ the QLQ-F17 as a generic tool without losing comparability to studies using the QLQ-C30. Supplementing the QLQ-F17 with relevant symptom items from the EORTC Item Library allows for a time-efficient and flexible measurement strategy.