The simplified Chinese version of the Nonrestorative Sleep Scale in Chinese young adults and measurement invariance across language and age.

Background: To assess the psychometric properties of the simplified Chinese version of the Nonrestorative Sleep Scale (NRSS) in Chinese young adults and examine measurement invariance across language and age.

Methods: After cognitive debriefing, the simplified Chinese NRSS was administered to university students in mainland China in this cross-sectional survey (Study 1). The Pittsburgh Sleep Quality Index (PSQI), the Patient Health Questionnaire (PHQ-4), and sociodemographic characteristics were also self-reported. The sample was randomly split into two halves to examine the scale structure using exploratory factor analysis (EFA) and asses the psychometric properties of the identified structure by confirmatory factor analysis (CFA), respectively. Incorporating data from two additional studies (Study 2: a survey of Hong Kong Chinese adults; Study 3: a survey of mainland Chinese adolescents), multigroup CFA models were conducted to examine the measurement invariance across language and age, followed by a t-test to determine group differences once invariance was established.

Results: In the 570 participants of Study 1 (28.8% male, age 20.2 ± 1.5 years), the EFA revealed a four-factor structure. The root mean square error of approximation, comparative fit index, and standardized root mean square residual in the CFA model were 0.053, 0.995, and 0.054, respectively. The statistically significant correlations of NRSS with PSQI (r = - 0.61) and PHQ-4 (r = - 0.53) demonstrated the convergent validity of NRSS. The internal consistency of the whole scale was 0.84. Measurement invariance was concluded between traditional and simplified Chinese NRSS and between young adults and adolescents with the change of comparative fit index and root mean square error of approximation smaller than 0.010. The effect size (Cohen's d) of difference between mainland Chinese adults and Hong Kong Chinese adults ranged from 0.193 to 0.771, while that between mainland Chinese adults and adolescents ranged from 0.027 to 0.345.

Conclusion: The simplified Chinese 12-item NRSS is valid and reliable for assessing NRS among Chinese young adults, and it can be used to measure and compare NRS between individuals using simplified Chinese and traditional Chinese, as well as across different age groups within the simplified Chinese user population.