Reliability and validity of the Pittsburgh Sleep Quality Index in breast cancer patients.

PURPOSE: We aimed to assess the factor structure, internal consistency, test-retest reliability, and construct validity of the European Portuguese version of the Pittsburgh Sleep Quality Index (PSQI) in breast cancer patients. METHODS: This study was based on a cohort of breast cancer patients, among whom the PSQI was used to measure sleep quality three years after cancer diagnosis (N = 474). A sample of 62 participants underwent additional PSQI testing, wore a wrist actigraph for five consecutive days, and was reevaluated with the PSQI after one month. A confirmatory factor analysis, considering the components suggested by the principal component analysis (PCA), was performed to determine model fit. To evaluate internal consistency and test-retest reliability, Cronbach's alpha and intraclass correlation coefficient (ICC) were calculated, respectively. To assess construct validity, Spearman's correlation coefficients were computed between PSQI scores and actigraphy measures and other theoretical related constructs. RESULTS: PCA suggested one or two components. The latter showed better fit to the data, though the two factors were strongly correlated (r = 0.76) and internal consistency was not satisfactory for one of the factors. Regarding the one-factor model, internal consistency (Cronbach's alpha = 0.70) and test-retest reliability (ICC = 0.76) were adequate. Sleep duration, habitual sleep efficiency, and sleep disturbance dimensions were significantly correlated with the corresponding actigraphy measures; the PSQI global score derived from the one-factor model was more strongly correlated with subjective sleep complaints (r ≥ 0.60). CONCLUSIONS: The unidimensional construct of the European Portuguese version of the PSQI showed adequate reliability and validity among breast cancer patients.