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Unlike Article #1 previously reviewed, which used a laboratory test to assess impairment of skills related to driving in sleep apneics and narcoleptics, this article concerns actual drivers' experiences with sleepiness as they perceive it to have affected their driving.
The author comments that, while police reports rarely implicate drowsiness as a factor in accidents, various in-depth studies implicate drowsiness in 6%-30% of all accidents. As one cause of excessive daytime sleepiness, sleep apnea has been reported to double the risk of auto accidents in one study.
The present study used a self-report, mail questionnaire to assess the association of sleepiness and accidents in an unusually large sample of subjects--4,621, about half of the total group to whom questionnaires were mailed.
The questionnaire inquired about driving patterns, accident history, sleepiness at the wheel, snoring, age, body mass, collar size, and occupation. Part of the questionnaire included the Epworth Sleepiness Scale, which asks for the subject's estimate of the likelihood of falling asleep in various situations; possible scores range from 0 to 24.
Extensive statistical analyses using different models were undertaken but won't be detailed here. Overall, 29% of drivers said they had felt close to falling asleep at the wheel in the past year. Some predictable factors associated with this were: score on the Epworth Sleepiness Scale, annual mileage, time spent driving on freeways (vs. surface streets in built-up areas), and willingness to drive for longer periods of time (such as four hours) without a break. Less predictable were findings of higher risk in drivers using company cars, and lower risk in older drivers.
Accidents in the past three years were reported by 18%, but only 12% of these involved injuries. Older age (up to 65+) was associated with fewer accidents. More accidents were associated with higher mileage, driving company cars, and falling asleep at the wheel. Drivers reported tiredness as a factor in 7% of accidents, contrasted to inattentiveness in 24% and misjudgment in 15%. Unlike other self-identified accident factors, tiredness showed consistent relationships to driving on freeways, younger age, and time of day--being most frequent at night (midnight to 7 a.m.), least frequent in the morning and rising again in the afternoon and evening.
Based on statistical adjustment of the data, the author concluded that 9-10% of all accidents were sleepiness related, a figure lower than that reported in other studies, but he noted that the majority of the accidents reported in his study did not result in injuries, and there is evidence that sleepiness is more often a factor in more serious accidents, where it may be a factor in 10-15%. He considered the consistent relationships of sleepiness at the wheel causing accidents to other factors to represent "a convincing indication that sleepiness is indeed a significant factor in accidents."
On average, snorers had a 30% higher risk of accidents than non-snorers (in another study, those who snored "often" had a 140% higher risk of accidents). In the present study, those who had felt close to falling asleep at the wheel had a 50% higher risk of accidents. However, obesity by itself--though related to daytime sleepiness--did not add anything to the risk.
The very large size of the sample in this study allowed for more convincing statistical analyses of accident predictors than the usually smaller size of most studies. On the other hand, the fact that only half of all potential subjects contacted actually returned the questionnaire raises the question of whether this sample is biased, that is to say, not representative of the total population of drivers. The author defends the representativeness of his sample by pointing out that their overall injury accident rate was similar to that in the general population, and the distribution of accidents by time of day was also similar, but this not enough to completely convince me. For example, drivers who have come close to having accidents, or who have had unrecorded, noninjurious accidents due to sleepiness, may be less ready to report this in a questionnaire obviously relating accidents to sleepiness, despite whatever reassurances might have been given that their reports would not affect their licensure.
If so, this study would underestimate the frequency of "minor" accidents due to sleepiness. Nor did the study assess the frequenc of near-accidents, often inquired about by sleep doctors as a warning sign of impaired driving. Finally, one could question the ability of subjects to correctly identify the cause of an accident--for example, inattentiveness could represent an effect of reduced alertness, as could misjudgment, without being accurately perceived as such. This also would lead to underestimation of sleepiness as a factor in accidents.
Of course, merely by identifying sleepy drivers the author cannot identify sleep apneics, since sleepiness may have many causes. However, his finding of snoring as a factor in accident risk does suggest that apnea is one of the causes of accident-related sleepiness.
Although I can't disagree with the author's conclusion that sleepiness--and presumably apnea as one of its major causes--is a factor in auto accidents, and I even suspect the frequency to be higher than the 10% suggested by the author, I do find it reassuring that the frequency does not seem so high that the public should conclude, for example, that apneics shouldn't drive. In fact, the decreasing risk of accidents with advancing age seems to me consistent with my impression that people who know themselves to have some impairment take extra care in their driving. For instance, a person who knows himself to have sleep apnea may limit the duration of his driving, and especially avoid long drives on freeways, or late at night, circumstances where the risk is highest. And, of course, diagnosed and treated apneics might be expected to be more aware than the average person of the degree of their sleepiness, and their lack of control over this symptom when it occurs, so that they may be less likely to undertake driving under those conditions.
WHAT DO YOU THINK ABOUT THIS ARTICLE AND MY COMMENTS?
CAN YOU RELATE THIS MATERIAL TO ANY PERSONAL EXPERIENCES?
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