Table 2.
Crosstabulation of sleep efficiency with demographic, lifestyle, and work factors
| Sleep efficiency | ||||
| High SE | Low SE | |||
| n (%) or
Mean ± SD |
n (%) or
Mean ± SD |
p | ||
| Age | 42.8 ± 11.0 | 42.8 ± 11.7 | 0.99 | |
| Sex | (Male) | 147 (34.8) | 155 (57.4) | <0.01 |
| Body mass index (kg/m2) | 22.0 ± 3.4 | 22.8 ± 3.3 | <0.01 | |
| Lifestyle habit | ||||
| Longer sleeping hours on weekends than on weekdays | (Yes) | 186 (44.0) | 99 (36.7) | 0.07 |
| Nightcap | (Yes) | 104 (24.6) | 76 (28.1) | 0.34 |
| Smoking | (Current smoker) | 32 (7.6) | 26 (9.6) | 0.41 |
| Exercise habits | (More than once a week) | 76 (18.0) | 59 (21.9) | 0.25 |
| Smartphone use at bedtime | (Yes) | 251 (59.3) | 183 (67.8) | 0.03 |
| TV watching in the bedroom | (Yes) | 123 (29.1) | 74 (27.4) | 0.70 |
| Water ingestion at bedtime | (Yes) | 340 (80.4) | 240 (88.9) | <0.01 |
| Ingestion of a caffeinated beverage | ||||
| Coffee | (More than one cup per day) | 304 (71.9) | 182 (67.4) | 0.24 |
| Green tea | (More than one cup per day) | 193 (45.6) | 128 (47.4) | 0.70 |
| Tea | (More than one cup per day) | 82 (19.4) | 54 (20.0) | 0.92 |
| Energy drink | (More than one cup per day) | 8 (1.9) | 10 (3.7) | 0.22 |
| Shift worker | (Yes) | 34 (8.0) | 29 (10.7) | 0.28 |
| Commuting time (hours) | 0.53 ± 0.38 | 0.61 ± 0.64 | 0.04 | |
| Brief Scale for Job Stress | ||||
| Workload | 2.1 ± 0.8 | 2.2 ± 0.8 | 0.20 | |
| Mental workload | 2.1 ± 0.7 | 2.3 ± 0.8 | <0.01 | |
| Problems in personal relationships | 1.9 ± 0.8 | 1.9 ± 0.8 | 0.61 | |
| Job control | 2.9 ± 0.8 | 2.9 ± 0.7 | 0.58 | |
| Reward from work | 2.9 ± 0.8 | 3.0 ± 0.8 | 0.04 | |
| Support from colleagues and superiors | 3.0 ± 0.7 | 3.0 ± 0.7 | 0.20 | |
Average and standard deviation (SD) for continuous data, percentage for categorical data and P-values are shown. Statistical analyses were conducted using the t test and chi-square tests.
SE: sleep efficiency
χ2 test or t-test, n = 693.