Factor analysis of the Pittsburgh Sleep Quality Index in breast cancer survivors

Sleep is a significant problem in breast cancer survivors (BCS) and measured frequently using the Pittsburgh Sleep Quality Index (PSQI). Thus, it is important to evaluate its factor structure. The two-process model of sleep regulation was the theoretical framework for this study.

To perform a confirmatory factor analysis of the PSQI in BCS and compare results between African-American and Caucasian BCS.

This was a secondary analysis of cross-sectional data using local and regional health care facilities and Eastern Cooperative Oncology Group referrals. The study included 1174 nondepressed BCS (90% Caucasian), with a mean age of 57 years and median PSQI global scores at the cutoff for poor sleep (median=6.00, interquartile range=4.00-9.00). Measurements included self-reported demographics, medical history, depression, and sleep.

Acceptable fit was not reached for the traditional one-factor model that would be consistent with current PSQI scoring or for alternative models in the published literature from other populations. A new two-factor model (i.e., sleep efficiency and perceived sleep quality) best fit the data but nested-model comparisons by race showed different relationships by race for 1) sleep quality-sleep latency and 2) sleep efficiency-sleep quality.

Results were inconsistent with current PSQI scoring that assumes a single global factor and with previously published literature. Although a new two-factor model best fit the data, further quantitative and qualitative analyses are warranted to validate our results in other populations before revising PSQI scoring recommendations. Additional recommendations are described for research.