The PSQI is a self-report questionnaire that assesses sleep quality and disturbances over a 1-month time period. It contains 19 items divided into 7 components: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication, and daytime dysfunction. Scores from each component are added to yield a global PSQI score, with higher scores indicating poorer sleep quality.