2.4. Statistical analysis
Statistical descriptions were made using the mean, standard deviation for continuous variables, and percentage for categorical variables. Independent-sample t-test, one-way analysis of variance, and χ
2
-test were used to compare differences between groups where appropriate.
To identify related factors regarding sleep duration in our sampled adolescents, logistic regression analyses were performed, with ‘1’ for sleep duration <8.0 h and ‘0’ for sleep duration ≥8.0 h. Unadjusted odds ratios (OR) and 95% confidence intervals (CI) were calculated by univariate logistic regression (Supplementary Table S2). Adjustments were also made by multivariate regression models following a three-step procedure. Each model included additional variables to assess increasingly proximate determinants of sleep duration: first, a simple model (model I) adjusted only for demographic and socio-economic characteristics ( Tables 1–3 and Supplementary Table S3); second, variables regarding biological chronic health problems, psychosocial conditions, and family history of sleep disorders ( Table 1) or sleep environments, school schedules (Table 2) or daily activity and behavior routine and parents’ sleep habits ( Table 3) were further included (model II); finally, a full model (model III) was established by adjusting socio-economic and environmental factors, biological chronic health problems and psychosocial conditions, family history of sleep disorders, sleep environments, school schedules, daily activity and behavior routine, and parents’ sleep habits simultaneously. In addition, the multivariate linear regression analyses were also performed (Supplementar Tables S4–S6).
All analyses were performed using the Statistical Package for Social Sciences (SPSS) for Windows, version 15.0 (SPSS Inc., Chicago, IL, USA). Statistical significance was set at P < 0.05 (two-tailed).
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