The subjective meaning of sleep quality: a comparison of individuals with and without insomnia.

GOOD SLEEP QUALITY IS ASSOCIATED WITH A WIDE RANGE OF POSITIVE OUTCOMES SUCH AS BETTER HEALTH, LESS DAYTIME SLEEPINESS, GREATER well-being and better psychological functioning.1 Poor sleep quality is one of the defining features of chronic insomnia.2 Although the construct of sleep quality is widely used, a review of the empirical literature suggests that it is not yet fully understood. Indeed, Akerstedt, Hume, Minors, and Waterhouse3 noted that “there seems to be very little systematic knowledge as to what actually constitutes subjectively good sleep and how this should be measured” and Buysse et al.4 referred to sleep quality as a “complex phenomenon that is difficult to define and measure objectively.” Indeed, the empirical results highlight the complexity of sleep quality, particularly as it relates to patients with insomnia. Research studies have reported that “a history of chronic insomnia does not predict poor EEG sleep.”5 Similarly, sleep quality is not directly associated with sleep quantity. For example, a common finding in the literature is that self-reported sleep does not correlate well with PSG defined sleep.6 Indeed, Edinger and colleagues7 distinguished between two groups: a subjective insomnia group who met criteria for insomnia but had normal/nondisturbed sleep on PSG and a subjective normal sleeper group who met criteria for a “normal sleeper” but had objectively disturbed sleep. Psychological variables were found to distinguish between these two groups: the subjective insomnia group exhibited more depressed mood, anxiety and they held more dysfunctional beliefs about sleep, relative to the subjective normal sleeper. These findings highlight the complexity of sleep quality and the importance of understanding the subjective meaning of sleep quality. Accordingly, the broad aim of the present study was to contribute new data to improving understanding of the subjective meaning of sleep quality. The primary focus of previous research has been to identify correlates of sleep quality. A wide range of factors have been investigated that, for ease of description, can be grouped into three clusters. First, there have been a handful of investigations of the correlation between perceived sleep quality and PSG-measured sleep parameters. These studies have included older female normal sleepers,8 older adults with insomnia,9 young adult good and poor sleepers,10 and individuals with unipolar depression.11 The consensus to emerge is that poor sleep quality estimates are associated with reduced Stage 1 sleep and more Stages 3 and 4 sleep. Second, other studies have investigated the association between sleep quality and the subjective perception of sleep parameters. The results suggest that sleep quality is associated with subjective estimates of the ease of sleep onset,12 sleep maintenance,13–15 total sleep time,14 and early awakening.13,15 In addition, restlessness during the night,3,13,16 movement during sleep,15,17 and anxiety, tension, or calmness when trying to sleep15 have also been reported to be associated with sleep quality. Moreover, perceived depth of sleep is important with less perceived light sleep and more perceived deep sleep being associated with higher sleep quality.18 Finally, several studies have examined correlations between sleep quality and how the individual feels immediately on waking and during the day. The results indicate that sleep quality is associated with ease of waking,19 tiredness, sense of balance and coordination,19 clear-headedness,18 how rested, restored and refreshed one feels,13 and mood and physical feelings15 on waking. During the day, feelings of tiredness predicted poorer sleep quality and alertness predicted better sleep quality.19 Taken together, although some consensus has emerged from studies of PSG-measured sleep parameters, there have been few consistent results from the studies that have focused on subjectively estimated aspects of sleep. The variability in the results obtained to date may be attributable to differences across studies in (1) the list of potential correlates evaluated, (2) the vague use of terminology, with some studies using terms like “sleep satisfaction” or “depth of sleep” and others referring to “sleep quality” and (3) the samples employed; the majority of previous studies have recruited good or normal sleepers, with only a handful based on poor sleepers or individuals with insomnia. Gaining an improved understanding of the subjective meaning of sleep quality among individuals with insomnia is important. For example, although differences in Rechtschaffen and Kales scored EEG sleep may not always be evident in patients with insomnia, relative to normal sleepers,5 it is possible that a more sophisticated understanding of the subjective meaning of sleep quality may produce a better measure of sleep quality, which may correlate better with EEG sleep. Alternatively, objective and subjective assessments of sleep quality may reflect different processes and not be directly related.19 In addition, understanding the meaning of sleep quality for individuals with insomnia may turn out to be important for a full recovery from insomnia. This suggestion is made based on cognitive theories which highlight the importance of the perception of or meaning or interpretation attached an event as the critical cause of distress, as opposed to the event itself.20 To summarize, the broad aim of the present study was to conduct a detailed and systematic investigation of the subjective meaning of sleep quality among individuals who meet diagnostic criteria for insomnia compared with a group of normal sleepers. We sought (1) to determine which sleep quality variables are judged to be most important, (2) to use a qualitative approach to determine whether there are important variables influencing perception of sleep quality not covered in the existing research literature, and (3) to compare the insomnia and normal sleeper groups on the meaning of sleep quality. Three different but complementary empirical approaches were employed to index the meaning of sleep quality: (1) a “Speak Freely” procedure in which participants were asked to describe a night of good and a night of poor quality sleep, (2) a “Sleep Quality Interview” in which participants rated the importance of variables included in previous research on sleep quality, and (3) sleep diaries in which participants also answered questions about their sleep quality over seven consecutive nights. These methods were selected to give a varied view of the meaning of sleep quality from both retrospective and prospective viewpoints and to capitalize on the advantages of procedures that require participants to endorse items versus procedures that require responses to be generated.