Validation and psychometric properties of the Spanish version of the Quality of Life Scale (QOLS) in patients with fibromyalgia

Abstract

Fibromyalgia (FM) is a chronic disease associated with high disability levels, which in turn lead to low quality of life (QOL). The objectives of this study were to translate the Quality of Life Scale (QOLS) into Spanish and to assess its reliability and validity for its use in patients with FM. A total of 140 women are suffering from FM (52.87 ± 9.35 years old). All belonged to an association of FM patients (AFIXA, Jaén, Spain). The Spanish versions of the FM impact questionnaire (FIQ), the SF-36, and Beck's Depression Inventory were used to assess them. The construct's validity was checked by means of exploratory factorial analysis (varimax with Kaiser normalization). Test-retest reliability was assessed through intraclass correlation coefficient (ICC), and convergent validity through Spearman's correlation. Results show that Cronbach's alpha was 0.887, which revealed high internal consistency. The value of ICC for the QOLS total was 0.765 (95 % CI 0.649-0.843, p < 0.001). QOLS presented a significant Spearman's correlation (p < 0.01) with Beck's Inventory, with the physical and mental subtotals of SF-36 and with FIQ. The main component analysis and the varimax rotation revealed the convergence on three factors that account for 54.05 % of variance. Taking into account the severity of the disorder, significant differences (p < 0.05) appeared in QOLS, with moderately afflicted patients getting higher scores than the most severe cases. In conclusion, our study shows that the Spanish version of the QOLS is a reliable instrument, with a good convergent and discriminant construct validity, for measuring the QOL of Spanish FM patients.