Reliability and validity of the Spanish version of the Pittsburgh Sleep Quality Index (PSQI) in patients with fibromyalgia

Fibromyalgia (FM) is recognized as a common condition, characterized by widespread pain and associated with sleep disturbances and poor-quality sleep. The Pittsburgh Sleep Questionnaire Index (PSQI) is one of the most recommended instruments to measure sleep quality and sleep disorders. The purpose of our study was to translate the questionnaire into Spanish and to assess the psychometric properties of the Spanish version of the PSQI. A total of 138 women with FM belonging to a FM association (AFIXA, Andalusia, Spain) completed the study. Internal consistency and test-retest reliability were analyzed. Factorial analysis was performed for the PSQI components. Convergent validity of the PSQI was evaluated using Spearman's rank correlation coefficient with the Spanish versions of the Fibromyalgia Impact Questionnaire (FIQ) and the health survey short form-36 (SF-36). In our analysis, the Spanish version of the PSQI has shown a good internal consistency of the total score, with a Cronbach's alpha of 0.805, and an acceptable test-retest reliability, with a Spearman's correlation coefficient of 0.773 (p < 0.001), for the total score. A two-factor structure was generated by exploratory factor analysis, with a Cronbach's alpha of 0.866 for factor 1 and of 0.712 for factor 2. In convergent validity analysis, the PSQI total score showed a significant correlation (p < 0.01) with the FIQ total score and with the mental and physical health summaries scores of the SF-36. Our results show that the Spanish version of the PSQI provides a reliable instrument, with a good convergent validity for measuring sleep quality among Spanish FM patients.