Table 2. Results of the Statistical Analyses on Tiredness, Sleepiness, and Sustained Attention.
| Variable | Forward-rotating shift (n = 80), mean (SE)a | Backward-rotating shift (n = 64), mean (SE)a | Rotation | Shift | Rotation and shift interaction | Multivariate tests within-cell regressionb | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Morning | Afternoon | Night | Morning | Afternoon | Night | F 1,139 | P value | F 2,278 | P value | F 2,278 | P value | Wilks λ (Rao R9,328) | P value | |
| TSS score | 0.60 (0.03) | 0.63 (0.03) | 0.84 (0.03) | 0.65 (0.04) | 0.67 (0.04) | 0.88 (0.04) | 1.58 | .21 | 67.91 | <.001 | 0.02 | .98 | 0.76 (4.38) | <.001 |
| KSS score | 0.76 (0.02) | 0.73 (0.02) | 0.88 (0.02) | 0.89 (0.01) | 0.88 (0.01) | 0.99 (0.01) | 41.23 | <.001 | 43.29 | <.001 | 0.59 | .55 | 0.92 (1.30) | .23 |
| PVT | ||||||||||||||
| Median RT | 2.46 (0.01) | 2.47 (0.01) | 2.49 (0.01) | 2.54 (0.01) | 2.54 (0.01) | 2.57 (0.01) | 42.12 | <.001 | 7.78 | <.001 | 0.06 | .94 | 0.92 (1.17) | .31 |
| Slowest 10% | 2.80 (0.03) | 2.71 (0.02) | 2.75 (0.03) | 2.89 (0.03) | 2.86 (0.03) | 2.89 (0.03) | 13.77 | <.001 | 3.26 | .04 | 1.73 | .18 | 0.94 (0.97) | .46 |
| Fastest 10% | 2.34 (0.01) | 2.34 (0.01) | 2.36 (0.01) | 2.44 (0.01) | 2.42 (0.01) | 2.45 (0.01) | 97.07 | <.001 | 10.18 | <.001 | 1.17 | .31 | 0.96 (0.66) | .74 |
| Minor lapses | 0.45 (0.04) | 0.35 (0.04) | 0.43 (0.04) | 0.69 (0.05) | 0.73 (0.04) | 0.85 (0.04) | 46.29 | <.001 | 4.37 | .01 | 3.581 | .02 | 0.93 (1.13) | .34 |
| Major lapses | 0.18 (0.02) | 0.06 (0.02) | 0.11 (0.02) | 0.22 (0.04) | 0.23 (0.04) | 0.21 (0.04) | 6.76 | .01 | 2.79 | .06 | 4.13 | .02 | 0.92 (1.35) | .21 |
| False starts | 0.36 (0.03) | 0.41 (0.03) | 0.33 (0.03) | 0.58 (0.05) | 0.62 (0.04) | 0.47 (0.05) | 19.83 | <.001 | 6.61 | .002 | 0.96 | .38 | 0.95 (0.82) | .59 |
| RT distribution | 1.37 (0.02) | 1.39 (0.01) | 1.43 (0.01) | 1.51 (0.01) | 0.51 (0.01) | 1.53 (0.01) | 60.13 | <.001 | 8.88 | <.001 | 2.73 | .07 | 0.98 (0.24) | .99 |
| Speed | 0.64 (0.01) | 0.65 (0.01) | 0.63 (0.01) | 0.59 (0.01) | 0.58 (0.01) | 0.57 (0.01) | 56.90 | <.001 | 8.80 | <.001 | 0.28 | .75 | 0.93 (1.13) | .34 |
Abbreviations: KSS, Karolinska Sleepiness Scale; PVT, Psychomotor Vigilance Task; RT, reaction time; TSS, Tiredness Symptoms Scale.
a
Data are log(1 + x) values and results of the rotation (forward or backward) by shift (morning, afternoon, or night) analysis of covariance values of the dependent measures (TSS, KSS, and variables of the PVT), considering Pittsburgh Sleep Quality Index score, age, and years on the job as covariates.
b
Sex, Pittsburgh Sleep Quality Index scores, age, and years on the job were used as covariates.