Structure validity of the Pittsburgh Sleep Quality Index in renal transplant recipients: A confirmatory factor analysis

The primary aim of this study was to fit and test the hypothesized three-factor model of the Pittsburgh Sleep Quality Index (PSQI) reported by Cole (2006) in renal transplant (RTx) recipients. We conducted a cross-sectional descriptive study using a convenience sample of home-dwelling RTx recipients, transplanted 6 months to 5 years prior to initiation of the study. Of the 135 RTx patients meeting the inclusion criteria, 29% were women with a mean age of 52 years (SD: 12; range: 21 to 76). The PSQI and a structured demographic questionnaire were mailed to the patients' homes. We conducted a confirmatory factor analysis to fit and test a single-factor model proposed by Buysse (1989) as well as the Cole (2006) three-factor model. Confirmatory factor analysis provided weak empirical support for the three-factor model (chi 2 = 16.555, d.f. = 8, P < 0.0351; RMSEA = 0.089; WRMR = 0.492; CFI = 0.983). Post hoc exploration of the three-factor model indicated the inclusion of an additional path from sleep-medication items to the factor of sleep efficiency, which demonstrated an improved fit (chi 2 = 11.850, d.f. = 8, P = 0.408; RMSEA = 0.060; WRMR = 0.384; CFI = 0.992). Confirmatory factor analysis suggests that the three-factor model of the PSQI has a better fit than the original one-factor model, and the additional pathway may improve its fit. The three-factor model with the additional path should be tested in a new sample before use in RTx recipients.