Table 1.
Descriptive statistics and psychometric properties of all outcome variables at baseline.
| Mean | SD | Items | α | Range |
Skewness | Kurtosis | ||
|---|---|---|---|---|---|---|---|---|
| Potential | Actual | |||||||
| Insomnia (ISI) | 4.80 | 3.55 | 4 | 0.71 | 0–16 | 0–16 | 0.75 | 0.13 |
| Sleep quality (PSQI) | 34.86 | 7.73 | 7 | 0.71 | 7–56 | 7–56 | −0.34 | 0.35 |
| Sleep onset latency | 25.75 | 25.26 | 1 | — | 0+ | 0–180 | 2.30 | 6.74 |
| Number of awakenings | 0.80 | 1.26 | 1 | — | 0+ | 0–10 | 2.71 | 10.63 |
| Depressive symptoms (CES-D) | 9.48 | 7.31 | 15 | 0.87 | 0–45 | 0–42 | 1.18 | 1.49 |
| Quality of life (SWLS) | 14.66 | 3.43 | 3 | 0.78 | 3–21 | 3–21 | −0.63 | 0.19 |
| Perceived stress (ASQ) | 69.52 | 18.02 | 30 | 0.89 | 30–150 | 30–122 | 0.26 | −0.53 |
| Mental toughness (MTQ) | 58.43 | 6.59 | 18 | 0.70 | 18–90 | 39–85 | 0.23 | 0.87 |
Abbreviations: 0 + = potential values can be equal to or greater than 0; ASQ = Adolescent Stress Questionnaire; CES-D = Centers for Epidemiologic Studies Depression Scale; ISI = Insomnia Severity Index; MTQ = Mental Toughness Questionnaire; PSQI = Pittsburgh Sleep Quality Index; SWLS = Satisfaction with Life Scale.