Psychometric performance of the CFQ-R-8D compared to the EQ-5D-3L and SF-6D in people with cystic fibrosis

Objective

This study aimed to compare the psychometric performance of the Cystic Fibrosis Questionnaire–Revised–8 Dimensions (CFQ-R-8D), a new, condition-specific, preference-based measure, with that of generic preference-based measures EQ-5D-3L and Short Form 6 dimensions (SF-6D).

Methods

Data from three trials of participants with CF aged ≥ 14 years who completed the CFQ-R and EQ-5D-3L or SF-6D were used. Analyses were undertaken to evaluate convergent validity based on correlations with CFQ-R domain scores. Known-group validity was assessed based on percent predicted forced expiratory volume in one second and pulmonary exacerbations. Responsiveness was based on correlation of change and sensitivity to change based on change in symptom severity. Effect sizes and standardized response means were estimated.

Results

CFQ-R-8D utilities and dimensions were strongly correlated with most of the overlapping CFQ-R domain scores (ρ > 0.5); EQ-5D-3L and SF-6D utilities and dimensions had moderate (ρ > 0.3) to strong correlations in dimensions capturing similar concepts. All measures showed evidence of known-group validity (P < 0.05). Change correlations were strong for CFQ-R-8D utilities and dimensions and CFQ-R, but they were moderate for SF-6D and mostly weak ((ρ > 0.1) for EQ-5D-3L. The SF-6D had the largest mean change over time and effect sizes, followed by CFQ-R-8D and then EQ-5D-3L. Neither CFQ-R-8D or SF-6D utility scores had ceiling effects (< 9% responses in full health) compared with those of EQ-5D-3L (61-62%). In participants classified as being in full health by EQ-5D-3L, CFQ-R-8D captured CF-specific health problems, particularly cough, abdominal pain, and breathing difficulty.

Conclusions

The CFQ-R-8D reflected known-group differences and changes over time with stronger evidence of good psychometric performance than EQ-5D-3L and similar evidence as SF-6D. Additionally, the CFQ-R-8D captured more condition-specific symptoms than EQ-5D-3L or SF-6D, which are important determinants of health-related quality of life for people with CF.