Objective: To cross-culturally adapt the LupusQoL into French, to test its measurement properties and to further investigate its domain structure.
Methods: The cultural adaptation process according to guidelines and pre-testing resulted in the LupusQoL-FR. SLE patients completed the LupusQoL-FR at baseline, 15 days, 3 months and 6 months. Validity was studied through content and construct validity (factorial and Rasch analysis for structural validity, Spearman's correlation and Mann-Whitney tests for external validity). Cronbach's α and intra-class correlation coefficients were computed for reliability. The standardized response mean was computed to evaluate responsiveness.
Results: In all, 182 patients, age 39.6 (10.6) years, mostly outpatients [mean SELENA-SLEDAI 2.6 (3.5)] were recruited. Factor analysis with eight imposed factors was very close to the original LupusQoL. A screeplot with parallel analysis showed that LupusQoL domains could be aggregated in two physical and mental scales. Both eight- and two-factor structures showed a good Rasch fit, internal consistency (Cronbach's α: 0.85-0.95), and test-retest reliability (intra-class correlation coefficient 0.79-0.95). External convergent (correlation with SF-36, r=0.59-0.78) and divergent validity (according to SELENA-SLEDAI) were also satisfactory.
Conclusion: The LupusQoL-FR is valid to assess quality of life in SLE patients. A two-factor structure of physical and mental aggregated scales is a valid alternative to the original eight-domain structure.