Original ArticleSleep quality in the general population: psychometric properties of the Pittsburgh Sleep Quality Index, derived from a German community sample of 9284 people
Introduction
Many diseases are associated with poor sleep, for instance: cancer [1], [2], [3], heart failure [4], [5], depression and generalized anxiety disorder [6], schizophrenia [7], dementia [8], and sarcoidosis [9]. Sleep deprivation is a stressor with consequences for the brain, including: reduced cognitive functioning [10], and chronic pain resulting in poor sleep [11]. Diurnal sleepiness may be a consequence of poor sleep quality and contribute to accidents [12], [13] as well as reduced cognitive performance [14].
Sleep disturbances are also frequently found in the general population. Prevalence rates of poor sleep quality range between 10 and 48% [15], [16], depending on the criteria and measurement techniques used. Objective measures for sleep quality, such as polysomnography or electroencephalographic spectral component analysis, provide reliable data, but they are often impractical as research tools in large-scale studies. Questionnaires are the convenient alternative.
The Pittsburgh Sleep Quality Index (PSQI) [17], developed by Buysse and colleagues in 1998, is probably the most often used self-report instrument for assessing sleep quality. It consists of 19 items and seven clinically relevant domains of sleep difficulties: subjective sleep quality, sleep latency, sleep duration, sleep efficiency, sleep disturbances, use of sleep medication, and daytime dysfunction. A global score of overall sleep quality can be calculated by adding up the single scores of these dimensions, producing scores ranging from 0 to 21. Global scores >5 are generally used to indicate poor sleep. According to this criterion, 32% of the Austrian general population [18] and 39% of the general population of Hong Kong [16] are bad sleepers. Psychometric properties of the PSQI have been examined in multiple studies: internal consistency [19], test–retest reliability [20], validity [8], [21], [22], [23], and factorial structure [24], [25], [26], [27]. The PSQI has been used in different cultures such as in Japan [7], China and Hong Kong [16], [28], Nigeria [29], and Brazil [30].
Normative studies are essential to compare the results of patient studies of the general population. Sometimes studies of patients include control groups, but these control groups often have low sample sizes [7], [23]. Therefore, it is mandatory to have comprehensive information about sleep quality in the general population. Some studies have already applied the PSQI to rather large samples in Austria [18], [31], [32], Hong Kong [16], and the USA (age ≥70 years) [19], [22], [33]. For clinicians, it will not only be interesting to know the mean scores but also the percentiles, especially in the upper part of the scale. In addition, it is important to understand the association between sociodemographic factors (socioeconomic level, professional status) and behavioral factors (tobacco and alcohol use) and sleep quality. Several studies have found associations between sleep quality and obesity [34], [35], [36], but it is worth analyzing this relationship in more detail. In addition, it is well known that bad sleep quality is associated with quality of life, fatigue, anxiety, and physical complaints, but a precise comparison of these associations beyond significance testing is also important for a better understanding of the psychosomatic burden of bad sleepers.
Therefore, the aims of this study based on a large sample of a community dwelling population in Germany were:
- (1)
To provide reference values of the PSQI and to test its psychometric properties.
- (2)
To examine the influence of sociodemographic and behavioral factors on sleep quality.
- (3)
To investigate the construct validity of the PSQI.
Section snippets
Sample
The LIFE-Adult-Study of the Leipzig Center for Civilization Diseases (LIFE) is a population-based study with a representative sample of people living in the city of Leipzig, Germany, with about 550,000 inhabitants. From the local residents’ registration office, an age-stratified and gender-stratified random selection of inhabitants, ranging in age from 18 to 80 years, was obtained. According to the study protocol, the focus was on the age group 40–80 years; the 18–39 years age range was
Sample characteristics
The total sample of the study program comprised 10,000 people. Details of the sampling procedure have been reported elsewhere [37]. The response rate of the study was 33%. Of the 10,000 people included in the total study, 9380 filled in the PSQI, at least in part. The remaining 620 subjects did not take part in the psychometric part of the examination. If only one PSQI subscale was missing, it was replaced with the rounded mean of the other subscales. Following this procedure, valid data were
Discussion and conclusions
The total mean score (M = 5.00) of this study was slightly higher than in the Austrian normative study from 2000 [18] (M = 4.51) and lower than in the normative study of Hong Kong [16] (M = 5.30). According to the generally accepted criterion for bad sleep quality (PSQI >5), 35.9% of the present German sample slept badly, compared with 32.1% in Austria and 39.4% in Hong Kong. Another German study with 753 people from the German general population [36] found that 34.7% were bad sleepers, which
Conflict of interest
The authors declare that they have no competing interests.
The ICMJE Uniform Disclosure Form for Potential Conflicts of Interest associated with this article can be viewed by clicking on the following link: http://dx.doi.org/10.1016/j.sleep.2016.03.008.
Acknowledgements
This publication is supported by LIFE – Leipzig Research Centre for Civilization Diseases – an organizational unit affiliated to the Medical Faculty of the University of Leipzig. LIFE is funded by means of the European Union, by the European Regional Development Fund (ERDF) and by funds of the Free State of Saxony within the excellence initiative (project numbers 713-241202, 14505/2470, 14575/2470).
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