Evaluation of Measurement Properties and Differential Item Functioning in the English and French Versions of the University of California, Los Angeles, Loneliness Scale‐6: A Scleroderma Patient‐Centered Intervention Network (SPIN) Study

OBJECTIVE: Loneliness has been associated with poorer health-related quality of life but has not been studied in patients with systemic sclerosis (SSc). The current study was undertaken to examine and compare the psychometric properties of the English and French versions of the University of California, Los Angeles, Loneliness Scale-6 (ULS-6) in patients with SSc during the COVID-19 pandemic. METHODS: This study used baseline cross-sectional data from 775 adults enrolled in the Scleroderma Patient-Centered Intervention Network (SPIN) COVID-19 Cohort. Reliability and validity of ULS-6 scores overall and between languages were evaluated using confirmatory factor analysis (CFA), differential item functioning (DIF) through the multiple-indicator multiple-cause (MIMIC) model, omega/alpha calculation, and correlations of hypothesized convergent relationships. RESULTS: CFA for the total sample supported the single-factor structure (comparative fit index [CFI] 0.96, standardized root mean residual [SRMR] 0.03), and all standardized factor loadings for items were large (0.60-0.86). The overall MIMIC model with language as a covariate fit well (CFI 0.94, SRMR 0.04, root mean square error of approximation 0.11). Statistically significant DIF was found for 3 items across language (β_item2  = 0.14, P < 0.001; β_item4  = -0.07, P = 0.01; β_item6  = 0.13, P < 0.001), but these small differences were without practical measurement implications. Analyses demonstrated high internal consistency with no language-based convergent validity differences. CONCLUSION: Analyses demonstrated evidence of acceptable reliability and validity of ULS-6 scores in English- and French-speaking adults with SSc. DIF analysis supported use of the ULS-6 to examine comparative experiences of loneliness without adjusting for language.