Validation of the Portuguese version of the Pittsburgh Sleep Quality Index (PSQI-PT)
Introduction
Sleep is a complex and dynamic behavioural state that greatly influences our waking hours and contributes to the body´s physical and mental recovery. Sleep disturbances currently prevail in society (Akerstedt and Nilsson, 2003). The most common sleep disorders are, namely, insomnia, restless legs syndrome, obstructive sleep apnea syndrome and shift wake–sleep disorder. These are some of the main health complaints of clinical and non-clinical populations. In western countries the rates of self-reported insomnia range between 10% and 48% (Ford and Kamerow, 1989, Mellinger et al., 1985, Ohayon and Paiva, 2005, Ohayon and Smirne, 2002). In Portugal, 28,1% of the population of 18 and more suffer from insomnia symptoms at least three nights a week (Ohayon and Paiva, 2005). The United Kingdom has up to one-third of adults living with some sleep disturbance (Ohayon et al., 1997) and in the USA more than 60 million (Chilcott and Shapiro, 1996).
Sleep disturbances are frequently associated with other health impairments as, daytime fatigue, mood disturbances, impaired memory and concentration (Colagiuri et al., 2011a). There are other studies that relate poor sleep quality and psychiatric disorders (Baglioni et al., 2014a, 2014b), cancer (Colagiuri et al., 2011b, Fortner et al., 2002, Savard and Morin, 2001) and diabetes (Buxton et al., 2012, Pan et al., 2011, Reutrakul et al., 2013). Daytime sleepiness has been associated with increased risk of motor vehicle accidents, worse physical health, and increased mortality risk (Buysse et al., 2005). Thus, poor sleep quality and insomnia symptoms are associated not only with worse mental and physical health but as well with increased absenteeism from work and health care costs and utilisation. The cost estimates regarding sick days, treatment and other impacts on society are considerable (Léger et al., 2002). On the basis of data from the American Institute of Medicine (IOM), hundreds of billions of dollars per year are spent on direct medical costs related to sleep disorders (Reis, 2014).
Sleep can be assessed across self-report, behavioural, physiological, circuit, cellular, and genetic levels of analysis (Buysse, 2014) by using quantitative parameters such as sleep duration, sleep latency and number of awakenings, and qualitative parameters which are merely subjective (Bertolazi et al., 2011). Polysomnography and/or electroencephalographic spectral content analysis obtain objective measurements of sleep quality although they demand an extensive time commitment from patients and financial effort for researchers (Hita-Contreras et al., 2014).
Haponik et al. (1996) realised in their study that no physician of primary care investigated for sleep disorders, though once they were trained on the disease, 82% of them started investigating it. Lack of information on sleep disorders in primary care medicine (Papp et al., 2002) and the difficulty in assessing objective and subjective sleep quality may represent some of the limitations encountered to understand the reality of sleep health. The use of a well-developed scale can facilitate the diagnosis of sleep disturbance at an early stage, therefore, enhancing the chances of prevention, recovery and diminishing concomitant outcomes.
Sleep quality is a multidimensional concept that includes individual components such as satisfaction with sleep, sleep efficiency, and impact on daytime functioning (Magee et al., 2008), thus, self-report retrospective and prospective questionnaires have been created to analyse subjectively sleep and its outcomes in clinical and non-clinical populations. These questionnaires can be used for clinical purposes, to aid on treatment responses, in clinical research and epidemiological studies (Bertolazi et al., 2011).
The Pittsburgh Sleep Quality Index is a 19-item self-rated questionnaire for evaluating subjective sleep quality in general and clinical populations over the previous month. Initially, it was developed for clinical populations with the purpose to provide a reliable, valid, standardised measure of sleep quality and to discriminate “good” and “poor sleepers” providing an easy questionnaire for patients to complete and for clinicians and researchers to interpret (Buysse et al., 1989a, 1989b). Aiming to overstep some of the several difficulties that other sleep questionnaires shared, Buysse (1989) pretended to develop an instrument with good clinimetric properties essential for the valid measurement of complex clinical phenomena (Feinsteein, 1987), as sleep quality. This questionnaire has been translated into 48 languages and has been used in a wide range of population-based and clinical studies (Buysse et al., 2008, 1989a, 1989b). It is easily understood, and it takes 5–10 min to be answered. It has been widely used to measure sleep quality in general population and, as well, in clinical groups, such as groups with psychiatric disorders (Baglioni et al., 2014a, 2014b), cancer (Colagiuri et al., 2011b, Fortner et al., 2002, Savard and Morin, 2001), respiratory diseases (Foley et al., 2004), fibromyalgia (Miró et al., 2011, Moldofsky, 2002).
As seen above, the Portuguese reality on sleeping difficulties outcomes is not that different from other western countries. The use of a well-designed self-report questionnaire as the PSQI can provide consubstantial information on the Portuguese actuality on sleep disorders and their effects. The PSQI was developed in 1988 and is the most commonly used generic measure in clinical and research settings (Mollayeva et al., 2016). It was validated for the Brazilian Portuguese spoken population in 2010 (Bertolazi et al., 2011). Until this day, to our knowledge, no other study has been made to validate the PSQI in Portugal. Although Brazil and Portugal share a common language, the fact is that there are cultural differences that need to be taken into account when trying to understand sleep effects. The adaptation and validation of any instrument need a cultural fit, that is, the instrument should be prepared to use in different cultural contexts (Beaton et al., 2000, Hambleton, 2005, Sireci et al., 2006).
Buysse (2014) later on in his research suggested the possibility of using the PSQI in non-clinical populations, aiming for more normal results. As well Mollayeva et al. (2016), in their review focused the importance of assessing the quality of this test in non-clinical populations. Their results confirmed that in non-clinical and clinical samples with known differences in sleep quality, the PSQI global scores, and all subscale scores, with the exception of sleep disturbance, differed significantly. The fact that we chose a non-clinical sample can represent a step forward in clinical and non-clinical populations’ prevention of sleep disorders as well as a tool for diagnosis and following treatment. Buysse (2014), highlighted the need to shift the focus of healthcare organisations from delivering health care to improve health. The present study was carried out to validate the PSQI for use in Portugal in a sample of Portuguese community-dwelling adults.
Section snippets
Pittsburgh quality sleep index
The PSQI assesses sleep quality over a one-month period. The questionnaire consists of 19 self-related questions and five (5) questions that should be answered by bedmates or roommates. These last five questions are used only for clinical information and, therefore, they are not tabulated in the scoring as well as reported in this article. The 19 self-related questions are categorised into seven (7) components, graded on a score that ranges from 0 to 3. The PSQI components are the following: 1)
Structural-adaptation
No structural modifications to the questionnaire were necessary during the cross-cultural adaptation process. All items were understandable and clear for a previous group of 20 people who were asked about the items.
Characteristics of the participants and their respective PSQI-PT scores
The total sample was concluded with 347 Portuguese community-dwelling adults aged 18–69 years who completed the questionnaire and were included in the study. The descriptive characteristics and its correlations are listed in Table 1. The 7-component score of the PSQI-PT had an
Discussion
The present study was carried out to validate the PSQI for application in Portugal in a sample of Portuguese community-dwelling adults. The scores for the PSQI-PT, measured by Cronbach's α coefficient components, showed an adequate internal consistency for each of the seven components of the questionnaire that assesses a particular aspect of sleep quality. Similar internal consistencies were obtained by other studies in other languages (Beaudreau et al., 2012, Magee et al., 2008, Mariman et
Acknowledgements
This study was supported by the Foundation for Science and Technology – Portugal (CIEO – Research Centre for Spatial and Organizational Dynamics, University of Algarve, Portugal). N.B. Becker received a doctoral fellowship from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES). Process BEX 1990/15-2.
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These authors contributed equally to this work.