Nonrestorative sleep : its evaluation, associated factors and impact

Abstract

Increasing evidence shows nonrestorative sleep (NRS) is a symptom of sleep, health, or psychiatric problem. It has been frequently reported in people with physical and psychological health issues but may not be comorbid with other sleep disorders. Around 8% of Hong Kong Chinese adults experienced NRS. However, there had been no standardized instrument for measuring NRS in Chinese populations, and the associated factors and potential impact have not been well studied. Therefore, this study aimed to (1) culturally adapt the Nonrestorative Sleep Scale (NRSS) in Chinese populations; (2) identify its associated factors; (3) examine its association with health-related quality of life (HRQL); and (4) shorten the NRSS. In accordance with international standards, I performed the linguistic and psychometric evaluation of the traditional Chinese NRSS with 120 participants. The traditional Chinese NRSS was essentially unidimensional and was reliable and valid for assessing NRS. The root mean square error of approximation (RMSEA), standardized root mean square residual (SRMR), and comparative fit index (CFI) of the bifactor confirmatory factor analysis (CFA) model were 0.06, 0.06, and 0.97, respectively. Convergent validity was demonstrated by the significant correlations with sleep quality (r = −0.66), insomnia (r = −0.65), depression (r = −0.54), and alertness (r = 0.68). The simplified Chinese NRSS was also culturally adapted. An exploratory factor analysis of 231 adolescents revealed a four-factor structure. The structure was confirmed in a CFA on another 250 adolescents, with the RMSEA, SRMR, and CFI being 0.06, 0.05, and 0.98, respectively. Convergent validity was demonstrated by the significant correlations with sleep quality (r = −0.62), insomnia (r = −0.71), depression (r = −0.60), and alertness (r = 0.54). Also, multigroup CFA models concluded measurement invariance across genders. The internal consistency and test-retest reliability were 0.83 and 0.86, respectively. In 500 Hong Kong Chinese adults recruited from a territory-wide household survey, the average NRS level was 64.77 on the 0–100 scale. People who had less NRS were those with more family income (estimate = 0.52), exercise (estimate = 1.19), and social support (estimate = 0.73) but had less somatic symptoms (estimate = −1.02), depression (estimate = −0.58), stress (estimate = −0.76), and noise sensitivity (estimate = −0.08). Furthermore, I have found that every unit increase in NRSS was significantly associated with 0.12 and 0.09 units increase in the physical and mental component scores, respectively, of the Short Form-12 Health Survey version 2. Lastly, I used the currently best approach of the optimal test assembly to obtain a 9-item traditional Chinese NRSS. The 9-item scale showed satisfactory internal consistency (Cronbach’s alpha: 0.819) and convergent validity by association with sleep quality (r = −0.59). The short form retained 92% of the test information of the original scale. Thresholds for the 12-item and 9-item scales were 68 and 66, respectively. Conclusively, the12-item and 9-item Chinese NRSS are reliable and valid for NRS assessment. Interventions incorporating exercise and social support and a remedy for somatic symptoms, stress, depression, and noise sensitivity are desirable. Such interventions would benefit NRS and improve HRQL.