The Spilsbury et al article1 looking at sleep behaviors in schoolchildren provides a welcome spotlight on a poorly understood area. A major criticism of the Spilsbury et al methods is that the study was not conducted for a significant length of time, just 7 days. Although the investigators attempt to reduce the effect of any confounders by removing data from children in the winter vacation, they do not in fact state which times of year the data were taken. Not including this information brings a significant degree of invalidity to the study since it is known that sleep duration can change with season,2 possibly via extraneous factors like temperature.3 A further possibility remains that variation in bedtimes measured in this study could be altered by cultural or social events since it is only 1 week that is measured. Spilsbury et al could have improved the quality of their study by conducting it over a greater number of weeks and stating the time of year the data were taken from, or even examining data from each individual at different times of the year.
Currie A. Sleep Behavior in an Urban US Sample of School-Aged Children: A Critical Appraisal. Arch Pediatr Adolesc Med. 2005;159(8):787-788. doi:10.1001/archpedi.159.8.787-a