Assessing the Factor Structure and Measurement Invariance of the Pittsburgh Sleep Quality Index Between Postmenopausal Breast Cancer Survivors and Controls.

Background and Purpose: This study evaluates the Pittsburgh Sleep Quality Index (PSQI) in terms of factor structure and measurement invariance (MI). The sample included postmenopausal breast cancer (BC) survivors (n = 101) and matched healthy controls (n = 60). Methods: Exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) were performed on PSQI's seven component scores. MI was tested between groups and across time using Bayes factor (BF). Results: Two factors were identified: sleep efficiency and perceived sleep quality. MI is evidenced between groups (BF < 0.007) and over time (BF > 150). Conclusions: PSQI scores with two subscales are comparable between postmenopausal BC survivors and controls over a 1-year period, providing some validation of PSQI for researching sleep quality in this population.