Sleep quality in the general population: psychometric properties of the Pittsburgh Sleep Quality Index, derived from a German community sample of 9284 people.

BACKGROUND: The Pittsburgh Sleep Quality Index (PSQI) is frequently used to assess sleep problems in patients. The aim of this study was to provide reference values for this questionnaire, to test psychometric properties, and to analyze associations with psychological, sociodemographic, and behavioral factors. METHODS: A German community sample comprising 9284 adult residents (aged 18-80 years) was surveyed using the PSQI and several other questionnaires. RESULTS: According to the generally accepted cut-off (PSQI > 5), 36% of the general population slept badly. Females reported significantly more sleep problems than males (mean scores: M = 5.5 vs. M = 4.4, respectively; effect size d = 0.35), but there was no linear association between age and sleep quality. Sleep problems were correlated with fatigue, quality of life (physical as well as mental), physical complaints, anxiety, and lack of optimism. Sleep quality was also strongly associated with socioeconomic status, professional situation (poorest sleep quality in unemployed people), and obesity. In addition to the results of the PSQI total score, mean scores of specific components of sleep quality were presented (sleep latency, sleep duration, and use of sleep medication). CONCLUSION: The PSQI proved to be a suitable instrument for measuring sleep quality. Gender differences, psychological factors, and obesity should be taken into account when groups of patients are compared with respect to sleep problems.