Components of quality of life in a sample of patients with lupus: a confirmatory factor analysis and Rasch modeling of the LupusQoL

The objective of this study was to test different exploratory solutions to the LupusQoL scale in a sample of Spanish patients with SLE using confirmatory factor analysis (CFA) and Rasch modeling, as well as to estimate the convergent validity. The chi(2) test, RMSEA, CFI, and TLI were used to test the fit of the different exploratory structures with CFA. To estimate the parameters in the dimensions found, a rating scale Rasch multidimensional random coefficient multinomial logit model was used. The reliability of the scores was obtained with coefficient alpha and coefficient omega. The convergent validity was calculated using Spearman's rho. Four hundred and fifty patients participated but complete data were available for 223 subjects. The original version (UK) and the French version obtained the best fit, showing that the proposed original structure was the best solution for the structure of the LupusQoL scale in the Spanish sample. The multidimensional solution of eight dimensions was adequate, but item 8 in physical health, item 16 in intimate relations, and items 29 and 30 obtained mean squares > 1.6. Internal consistency and coefficient omega of the scores in the eight domains were higher. The Spanish version of LupusQoL correlated strongly with the corresponding SLAQ, EQ5D analogic scale, and EQ5D domain. This analysis confirmed the structure of eight dimensions of the original version in patients with SLE.