Clinical reviewThe Pittsburgh sleep quality index as a screening tool for sleep dysfunction in clinical and non-clinical samples: A systematic review and meta-analysis
Introduction
Disturbed sleep is among the most frequent health complaints clinicians encounter ∗[1], [2]. It is common in the general population – more than one half of adults in the Western world experience intermittent sleep disturbances and between 15 and 20% of adults report chronic sleep problems [2]. Sleep dysfunction can lead to serious impairment in daytime performance [3], [4], increase the risk of involvement in motor-vehicle and occupational accidents [5], [6], exacerbate medical, neurologic, and/or psychiatric conditions [7], [8], and result in diminished quality of life [9]. In the past, sleep complaints were treated with hypnotic medications without further diagnostic evaluation [10]. The last three decades of research have culminated in the understanding of sleep dysfunction as a complex entity [11], ∗[12], wherein a range of primary sleep disorder symptoms overlap with neurophysiological, psychological, and behavioral factors, requiring targeted diagnostic and treatment intervention (Fig. 1).
The multifactorial construct of sleep dysfunction causes diagnostic confusion in determining which persons need to be extensively investigated for the etiology of their complaints to be established. Issues of self-insight and awareness are also important to note – some persons may not be fully aware of their sleep impairment and will thus not emphasize such issues in the physician's office, or do not appreciate the extent or impact of their sleep problems [13]. As such, the main challenge today for primary care and specialist clinicians is to identify the patients who may have undetected sleep dysfunction and to direct further diagnostic investigation. A tool for this purpose would be discriminative, according to criteria defined by Kirshner and Guyatt [14] and thus, should be evaluated by its 1) intra-rater reliability; 2) internal consistency and reliability; and 3) construct validity.
There are numerous instruments, both subjective and objective, that can be used to measure sleep functioning [15]. In objective measures, the expectation is limited involvement of personal judgment, that is, results are to be influenced neither by the person doing the measuring nor the person being measured. In subjective measurements, both roles can impact the outcome to some extent. Given that even objective measures have a subjective component, often requiring an expert to read and interpret the measures, many feel that a patient's opinion and appraisal of his or her own status is of great value [16]. This view is evident in the recent initiative of the US federal government, which seeks a balance between outcomes that are of interest to investigators (i.e., results of laboratory testing, etc.), and those of primary interest to the patient (i.e., satisfaction, self-perceived quality, etc.) in using patient reports of health status [17].
Self-perceived sleep quality represents something of a challenge to measure because there is no generally accepted reference or gold standard [18]. One approach would be to use a carefully constructed questionnaire incorporating the recommendations of the American Psychological Association pertaining to clinical sleep dysfunction evaluation [19]. This starts with the main complaints of a patient, classified into: 1) inability to get adequate nighttime sleep given the opportunity for sleep (i.e., insomnia), 2) negative daytime consequences as a result of poor sleep (e.g., daytime sleepiness, fatigue, and cognitive impairment), 3) episodic nocturnal movements or behaviors, or 4) a combination of these concerns.
Although no specific quantitative sleep parameters define insomnia disorder [20], an average sleep latency over 30 min, wake after sleep onset lasting more than 30 min, sleep efficiency less than 85%, and/or a total sleep duration of less than six and a half hours are common manifestations, when reported together with difficulty initiating or maintaining sleep, waking too early, or chronically non-restorative sleep, is considered clinically significant if occurring three or more nights per week, and suggestive of chronic insomnia disorder if lasting one or more months [21].
Reports of daytime impairment almost invariably accompany the report of inadequate nighttime sleep [18], and these symptoms are often the main complaints in patients seeking medical care. In many patients, daytime impairment will include excessive sleepiness, fatigue, low energy, low motivation, and/or cognitive symptoms related to poor attention, concentration, and memory.
Sleep-related movements and/or behaviors are often reported by the spouse or bed partner, as the patient is usually not aware of episodes such as snoring, twitching or kicking of legs, bruxism (i.e., teeth grinding), sleep walking or talking, or violent behaviors arising from sleep [18].
An ideal screening instrument would incorporate all items relevant to concept of sleep dysfunction, and be able to differentiate “good” and “poor” sleepers. Given the issues with self-insight and awareness in some persons, the descriptive tool would incorporate items for the significant other (i.e., bed partner or caregiver), including those related to behavioral manifestations in sleep.
The Pittsburgh sleep quality index (PSQI) [22] is the most commonly used generic measure in clinical and research settings. A search conducted in March of 2014 for PubMed articles containing “Pittsburgh sleep quality index” as a search term returned in total 1512 articles and a growth trend over time, with 141 articles published in 2010 and 323 articles published in 2013. By contrast, a search for “Leeds sleep evaluation questionnaire” [23] returned 66 articles in total; “sleep disorder questionnaire” [24] returned 52 articles, and “medical outcomes study sleep scale” [25] returned a total of 32 articles. The PSQI was developed in 1988, with no particular clinical population in mind, to: 1) provide a reliable, valid, standardized measure of sleep quality; 2) discriminate “good” and “poor” sleepers, and 3) provide an easy index for patients to complete and for clinicians and researchers to interpret [22]. Consequently, the developers' targeted concept and purpose conform to our measurement need (i.e., discriminate “good” and “poor” sleepers).
Given the PSQI's widespread use, a comprehensive review of its measurement properties is long overdue. Moreover, while individual papers examining the various aspects of the measurement properties of the PSQI have been published, its applicability to different clinical and non-clinical groups (i.e., persons with and without medical or psychological conditions, respectively) has not been examined. Therefore, we undertook a systematic review of the literature pertaining to the psychometric properties of the PSQI with the purpose of: 1) appraising the clinical sensibility of the instrument, 2) systematically evaluating its psychometric properties, specifically construct validity and reliability, and 3) summarizing sex-stratified results pertaining to the PSQI. Finally, this systematic review featured a meta-analytic component, reporting the weighted mean difference in PSQI global and subscale scores for clinical and non-clinical samples. The present work intended to provide information for both researchers and clinicians on the PSQI's ability to serve as a descriptive tool for sleep dysfunction in non-clinical and clinical populations, while also identifying pitfalls and providing ideas for future research utilizing the measure.
Section snippets
Search strategy
In collaboration with a medical information specialist (JB) and utilizing proposed PubMed search filters for finding studies on a measurement's properties [26], we utilized a comprehensive search strategy to study measure properties of the PSQI. Four electronic databases, MEDLINE, Embase, PsycINFO, and health and psychosocial instruments (HAPI, or HaPI), were searched. Table S1 displays the terms used in searches of each database.
Selection criteria
All English language peer-reviewed studies found through the
Search results
Of 1376 articles identified, 50 [9], ∗[22], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [47], [48], [49], [50], [51], [52], [53], [54], [55], [56], [57], [58], [59], [60], [61], [62], [63], [64], [65], [66], [67], [68], [69], [70], [71], [72], [73], [74], [75], [76], [77], [78], [79], [80] were selected for full-text review and 37 [46], [47], [48], [49], [50], [51], [52], [53], [54], [55], [56], [57], [58], [59], [60], [61], [62], [63], [64], [65], [66],
Sensibility
Since its development, the PSQI has been widely used in research and clinical practice, providing information on a respondent's sleep quality, discriminating “good” and “poor” sleepers, and in clinical assessment of a variety of sleep disturbances. Interestingly, the PSQI, conceptualized and developed as a clinimetric measure (i.e., aimed for all items to measure a particular aspect of a complex clinical construct in the absence of a gold standard for said construct; emphasis on heterogeneity
Conclusion
The PSQI is currently the only standardized clinical instrument that covers a broad range of indicators relevant to sleep quality. Items pertaining to circadian rhythm disorders and medication effects other than those by sleep aids, although not covered, may be inferred based on analysis of data from available items, together with a detailed clinical history of the patient. We found strong positive evidence for reliability and validity (hypothesis testing), and moderate positive evidence for
Conflict of interest
The authors have no conflict of interest or outside funding sources to disclose.
Acknowledgments
Our study had no external funding source. The first author was supported by 2012/2013 Toronto Rehabilitation Institute Scholarship, the Ontario Graduate Scholarship 2012/2013 and the 2013/2015 Frederick Banting and Charles Best Doctoral Research Award from the Canadian Institutes of Health Research. Angela Colantonio was supported by the Saunderson Family Chair in Acquired Brain Injury Research and the Canadian Institutes for Health Research Grant–Institute for Gender and Health. (#CGW-126580).
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