Table 5.
Optimal Thresholds for Predicting Adverse Outcomes and Associated Odds Ratios for Physiological Drowsiness Outcomes
| Item | Description | Threshold | Sens. | Spec. | OR [95% CI]β | p |
|---|---|---|---|---|---|---|
| Severe drowsiness event: JDS > 4.5 | ||||||
| KSS | Subjective sleepiness | 7 | 0.82 | 0.78 | 15.80‡ [4.3, 54.5] | <0.001 |
| LFA | Likelihood of falling asleep | 3 | 0.70 | 0.76 | 7.89‡ [2.6, 23.6] | <0.001 |
| SSQ1 | Struggle to keep eyes open | 3 | 0.94 | 0.78 | 40.15‡ [5.2, 310.1] | <0.001 |
| SSQ2 | Vision blurred | 4 | 0.76 | 0.88 | 25.26‡ [7.6, 84.3] | <0.001 |
| SSQ3 | Nodding off to sleep | 3 | 0.88 | 0.84 | 37.73‡ [8.2, 173.1] | <0.001 |
| SSQ4 | Difficulty keeping to middle of road | 3 | 0.94 | 0.72 | 43.58‡ [5.7, 334.2]β | <0.001 |
| SSQ5 | Difficulty maintaining correct speed | 3 | 0.94 | 0.72 | 40.15‡ [5.2, 310.1] | <0.001 |
| SSQ6 | Mind wandering | 6 | 0.81 | 0.93 | 33.23‡ [10.2, 108.7] | <0.001 |
| SSQ7 | reactions are slow | 3 | 0.88 | 0.78 | 26.96‡ [5.9, 122.5] | <0.001 |
| SSQ8 | Head dropping | 3 | 0.76 | 0.93 | 41.55‡ [12.0, 144.4] | <0.001 |
| SSQ global score | 24 | 0.88 | 0.86 | 44.20‡ [9.6, 203.9] | <0.001 | |
| Moderate drowsiness event: JDS > 2.7 | ||||||
| KSS | Subjective sleepiness | 5 | 0.59 | 0.71 | 3.69 [2.0, 6.7] | <0.001 |
| LFA | Likelihood of falling asleep | 3 | 0.47 | 0.83 | 4.49 [2.6, 8.6] | <0.001 |
| SSQ1 | Struggle to keep eyes open | 3 | 0.55 | 0.79 | 4.65 [2.5, 8.6] | <0.001 |
| SSQ2 | Vision blurred | 2 | 0.66 | 0.70 | 4.75 [2.6, 8.7] | <0.001 |
| SSQ3 | Nodding off to sleep | 2 | 0.61 | 0.74 | 4.53 [2.5, 8.3] | <0.001 |
| SSQ4 | Difficulty keeping to middle of road | 3 | 0.55 | 0.77 | 4.27 [2.3, 7.8] | <0.001 |
| SSQ5 | Difficulty maintaining correct speed | 2 | 0.69 | 0.52 | 2.44 [1.3, 4.4] | 0.003 |
| SSQ6 | Mind wandering | 3 | 0.59 | 0.68 | 3.10 [1.7, 5.6] | <0.001 |
| SSQ7 | Reactions are slow | 3 | 0.50 | 0.86 | 6.27 [2.2, 12.2] | <0.001 |
| SSQ8 | Head dropping | 3 | 0.28 | 0.95 | 8.36 [3.2, 21.9] | <0.001 |
| SSQ global score | 23 | 0.46 | 0.92 | 10.94 [5.0, 24.0] | <0.001 | |
| End-state fall asleep event: EEG microsleep | ||||||
| KSS | Subjective sleepiness | 6 | 0.59 | 0.69 | 3.19 [1.16, 8.78] | 0.029 |
| LFA | Likelihood of falling asleep | 3 | 0.65 | 0.76 | 6.17 [2.16, 17.62] | <.001 |
| SSQ1 | Struggle to keep eyes open | 4 | 0.53 | 0.82 | 5.11 [1.84, 14.18] | 0.002 |
| SSQ2 | Vision blurred | 3 | 0.53 | 0.78 | 3.84 [1.40, 10.53] | 0.015 |
| SSQ3 | Nodding off to sleep | 2 | 0.71 | 0.64 | 4.25 [1.44, 12.57] | 0.008 |
| SSQ4 | Difficulty keeping to middle of road | 3 | 0.53 | 0.67 | n.s | n.s |
| SSQ5 | Difficulty maintaining correct speed | 5 | 0.18 | 0.89 | n.s | n.s |
| SSQ6 | Mind wandering | 4 | 0.53 | 0.72 | n.s | n.s |
| SSQ7 | Reactions are slow | 3 | 0.42 | 0.74 | n.s | n.s |
| SSQ8 | Head dropping | 7 | 0.00 | 0.98 | n.s | n.s |
| SSQ global score | 16 | 0.71 | 0.63 | 4.15 [1.40, 12.27] | 0.009 | |
Dichotomous OR—change in odds of a severe/moderate event occurring in the next 15 minutes when the predictor value is above the identified threshold, compared to when below.
βOdds ratio calculated with Haldane-Anscombe Correction and significance via Fishers Exact Test.
‡Odds ratio is inflated due to low n in the false negatives section of the contingency table. Interpretation/reporting of the lower bound 95% confidence interval is recommended