Philip and colleagues have validated the conventional wisdom that coffee and napping improve nighttime highway driving performance with their real-life study. Their study raises several questions. First, an alternative factor affecting the ability to drive at night is nighttime visual acuity. One of the twelve study participants (participant number 7) was egregiously the worst under all three nighttime test conditions: 13 line crossings with coffee (3.1 SD worse than the mean), 17 line crossings with placebo (1.8 SD worse than the mean), and 8 line crossings with napping (2.0 SD worse than the mean). In contrast, during the day, his driving ability was comparable to the rest of the test subjects. Cataract disease, retinitis pigmentosa, and vitamin A deficiency are several conditions that may decrease nighttime visual acuity. While these disorders would certainly be highly unusual in a young healthy male and while there may be a large range in what is considered "normal" driving ability, it may be of interest to exclude these conditions as factors, given this participant’s consistently poor performance, rather than attributing it to simply fatigue. Nevertheless, when this driver is excluded from the analysis, an informal analysis of the remaining 11 subjects using paired t-tests with Bonferroni correction for multiple comparisons yields findings similar to the overall conclusions of the trial. Secondly, while the number of line crossings may be viewed as a proxy for driving performance, it would be of interest to know how many times the professional copilot had to intervene as a consequence. While potentially subjective, this may better capture the relevance of each line crossing, especially since the participants were instructed to drive at high speeds averaging 80 miles per hour. Finally, it would informative to know what measures the professional copilot driver used to stay awake for the study. Napping, coffee, or another intervention, like modafinil? (Author/publisher) The full report is titled “The Effects of Coffee and Napping on Nighttime Highway Driving. A Randomized Trial” (See C 36092 fo). It is in the 6 June 2006 issue of Annals of Internal Medicine (volume 144, pages 785-791). The authors are P. Philip, J. Taillard, N. Moore, S. Delord, C. Valtat, P. Sagaspe, and B. Bioulac. http://www.annals.org/cgi/content/abstract/144/11/785
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