The regression of the slopes of work demands and physical workload versus the slopes of fatigue and sleep problems (mixed-model regression)
| Work demand slope versus slope of | Work demands versus Coeff±SE | Z | P value | Physical workload versus Coeff±SE | Z | P value |
| Physical workolad | 0.204±0.031 | 6.5 | 0.000 | |||
| Fatigue | 0.106±0.010 | 10.9 | 0.000 | 0.010±0.004 | 2.4 | 0.018 |
| Sleep problems | 0.243±0.022 | 11.1 | 0.000 | 0.028±0.010 | 2.9 | 0.004 |
Adjusted for age and gender. *P<0.05; **P<0.01; ***P<0.001.